Fix issue with GL_UNSIGNED_INT_8_8_8_8[_REV] ...

I had incorrectly remembered and associated GL_UNSIGNED_INT_8_8_8_8 with
GL_RGBA/GL_UNSIGNED_BYTE.  The correct associated of GL_RGBA/GL_UNSIGNED_BYTE
is with GL_UNSIGNED_INT_8_8_8_8_REV.  The error caused the compoents to be
swizzled in an ABGR fashion.

This commit fixes that problem for both GL_RGBA and GL_BGRA.
Merge pull request #76 from IanAtLunarG/pxfmt_140528_Fix8888Rev

Fix issue with GL_UNSIGNED_INT_8_8_8_8[_REV] ...