GL: Fix half-float texture formats.

This matches the ps3 output/channels for these textures per the
rsx/texture_formats test.
GL: Fix X16 / Y16_X16 texture formats.

Per the rsx/texture_formats test.  Not sure about pitch, may need to deal
with UNPACK_ROW_LENGTH...
GL: Fix the compressed R8B8 / B8R8 type formats.

The not-swizzled bit is always set for them.
Merge pull request #247 from unknownbrackets/texformats

Implement more texture formats per the test