BGE: Fix for bugs #34428, #20856, #20281. These were all multi-uv bugs caused by the BGE keeping too much uv information. When setting up shaders the BGE assumes each UV layer is unique, but the converter would store duplicates.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54972 954f8c5b-7b00-dc11-b283-0030488c597c