Add configurable toggle that rounds vertices to the nearest pixel when

w=1.  This fixes some games at higher IRs.

Source/Core/VideoCommon/ConstantManager.h

@@ -45,6 +45,7 @@ struct VertexShaderConstants
   float4 normalmatrices[32];
   float4 posttransformmatrices[64];
   float4 pixelcentercorrection;
+  float4 viewport;
 };
 
 struct GeometryShaderConstants