Retina fix working now.

I had to enable NSHighResolutionCapable in Info.plist.
http://forum.openframeworks.cc/t/retina-detection-backingscalefactor/13087/3

Probably it is ok to keep it enabled even if you don't have retina display. but please double check
Merge pull request #4 from wasawi/master

Retina fix working now.