The present invention relates to an alloyed molten zinc plated steel sheet. TECHNICAL FIELD The present invention relates to a high strength, alloyed molten zinc plated steel sheet able to be utilized as a member of an automobile, building material, or electrical appliance and a process of production of the same. BACKGROUND ART In the auto industry, demand has been rising for steel sheet provided with the properties of both shapeability and high strength so as to achieve both lighter weight of the chassis to deal with environmental problems -and safety-in collisions. To deal with these needs, Japanese Unexamined Patent Publication (Kokai) No. 5-59429 discloses steel sheet having as the steel sheet structure a mixture of the three phases of the ferrite phase, bainite phase, and austenite phase and transforming the residual austenite to martensite at the time of shaping so as to utilize the transformation-induced plasticity exhibiting a high ductility. This type of steel sheet for example forms a complex structure by the addition, by wt%, of C: 0.05 to 0.4%, Si: 0.2 to 3.0%A, and Mn: 0.1 to 2.5% in the steel and controlling the temperature pattern in the process of annealing in the two-phase region, then cooling and is characterized in that the desired properties can be brought out without the use of expensive alloy elements. When zinc plating this steel sheet by a continuous molten zinc plating system, usually the surface of the steel sheet is degreased, the surface is cleaned, then, for the purpose of forming the above-mentioned structure, the sheet is heated in an nonoxidizing furnace to form an iron oxide layer of a thickness of 50 nm to 1µm or so on the surface of the steel sheet, annealing the sheet in a reducing furnace to reduce the iron oxide layer, then dipping the sheet in a molten zinc plating bath to plate it with zinc. When producing an alloyed molten zinc plated steel sheet, the steel sheet is dipped in a plating bath in that step, then held at a temperature of 400 to 600°C or so to alloy the zinc and iron and convert the plating layer to an alloy phase of Fe and Zn constituting an 8l phase. Steel sheet, however, contains large amounts of easily oxidizing elements such as Si and Mn compared with the ordinary deep drawn cold-rolled steel sheet etc., so there is the problem that the surface of the steel sheet is easily formed with Si oxides, Mn oxides, or Si and Mn complex oxides in the heat treatment performed in the above series of steps. However, in industrial scale systems, it is difficult to reduce the oxygen potential of the atmosphere in the heating step to an extent where Si or Mn will not be oxidized, so formation of Si and Mn oxides at the surface of the steel sheet is substantially unavoidable. Further, if the surface of the steel sheet is formed with an Si oxide layer or Mn oxide layer, there is the problem that the alloying of the Zn and Fe is inhibited in the alloying step at the time of production of the alloyed molten zinc plated steel sheet and parts where the Fe-Zn alloy phase have not yet been formed remain. One method easily conceivable as a means for solving these problems is to set the alloying treatment temperature slightly high to promote alloying of Fe and Zn. At the alloying treatment temperature of 450 to 600°C, however, austenitic transformation occurs in the steel sheet, so if setting the alloying treatment temperature slightly high, depending on the holding time, the structure of the steel sheet will not become the desired mixed structure of a mixture of the three phases of the ferrite phase, bainite phase, and austenite phase. As a result, there is the problem that the shapeability and strength of the steel sheet aimed at cannot be secured in some cases. To deal with this problem, Japanese Unexamined Patent Publication (Kokai) No. 55-122865 discloses the method of forming a 40 to 1000 nm iron oxide layer on the surface of a steel sheet in a heat treatment step by a nonoxidizing furnace in a continuous molten zinc plating step so as to prevent outward diffusion of the Si or Mn in the reduction step, suppress the formation of the Si oxide layer, and improve the plating properties. With this method, however, if the reduction time is too long for the thickness of the iron oxide layer, Si will become dense at the surface of the steel sheet and an Si oxide layer will be formed, while if the reduction time is too short, iron oxide will remain on the surface of the steel sheet and defects in the plating properties, that is, the formation of unformed parts of the Fe-Zn alloy phase will be formed. Further, in recent continuous molten zinc plating systems, annealing systems using radiant type heating furnaces rather than nonoxidizing furnaces are becoming the mainstream. In such systems, there was the problem that the above method could not be used. Further, Japanese Unexamined Patent Publication (Kokai) No. 2000-309824 discloses as a method for preventing selective oxidation of the Si or Mn at the time of annealing the method of hot rolling the steel sheet, then heat treating it in the state with the black skin scale still attached in an atmosphere where reduction will substantially not occur and in a temperature range of 650 to 950°C so as to form a sufficient internal oxide layer in the base iron surface layer. With this method, however, in addition to the conventional continuous molten zinc plating step, a heat treatment step for forming the internal oxide layer and a pickling treatment step become necessary, so there was the problem that a rise in production costs was invited. Further, the plated steel sheet having the internal oxide layer had the problem of easily peeling of the plating layer. DISCLOSURE OF INVENTION In view of the above problems, the present invention has as its object the provision of an alloyed molten zinc plated steel sheet wherein the area of the unformed parts of the Fe-Zn alloy phase in the plating layer is less than 10% of the area of the steel sheet as a whole and wherein the strength and shapeability are superior. Further, it has as its object the provision of a process of production of the alloyed molten zinc plated steel sheet at a low cost without modifying the system or adding steps in a conventional continuous molten zinc plating production system. To solve the above problem, the inventors engaged in intensive studies and as a result newly discovered that by including in the plating layer oxide particles of at least one type selected from an Al oxide, Si oxide, Mn oxide, Al and Si complex oxide, Al and Mn complex oxide, Si and Mn complex oxide, and Al, Si, and Mn complex oxide alone or in combination, alloying of the plating layer is promoted and uniform alloying across the entire surface of the steel sheet is obtained and made it possible to provide an alloyed molten zinc plating steel sheet wherein the area of the unformed parts of the Fe-Zn alloy phase in the plating layer is less than 10% of the area of the steel sheet as a whole and wherein the strength and shapeability are superior. The fundamental reason why addition of oxide particles in the plating layer causes alloying of the plating layer to be promoted and a uniform alloy layer to be obtained across the entire steel sheet is unclear, but the inventors continued with their intensive studies and as a result discovered that by making the plating layer the above structure, the alloying of Fe-Zn occurs uniformly across the entire surface of the steel sheet. Further, the inventors discovered that the above alloyed molten zinc plated steel sheet can be obtained by adjusting the ratio PH20/PH2 of the steam partial pressure and hydrogen partial pressure of the atmosphere in the reducing furnace in the recrystallization annealing step of a continuous molten zinc plating system to 1.4xlO'10T2-1.0xlO'7T+5.0xlO"° to 6 . 4xlO'V+l. 7xlO"