Screen/OSX: Remove -framework AGL, set macosx-version-min=10.6, no 32-Bit fontglue.

AGL is no longer needed.
Minimum OSX version for our mex files is now 10.6.

Remove 32-Bit parts of PsychFontGlue.c - The same code would build
on 32-Bit, but the minimum required system would be 10.5 or maybe
10.6.

Screen and FontInfo mex files for OSX rebuilt.