Psychopy OSX 64-bit compatibility added

Got psychopy to work on 64-bit OSX systems, with pyglet 1.2 alpha 1
Corrected system check for pyglet.lib overload
Another corrected platform check

This one slipped my attention for a minute
Platform checks done right this time
Merge pull request #561 from dschreij/pyglet-1.2alpha1

Psychopy OSX 64-bit compatibility added