Python 3 compatibilty (strings vs bytes, PNG tests)
Python 3 compatibilty (strings vs bytes, PNG tests)

Thanks to Claudio Canepa for the patch.

Fixes issue #724.

Alwnikrotikz/pyglet,google-code-export/pyglet,cledio66/pyglet,cledio66/pyglet,Austin503/pyglet,shaileshgoogler/pyglet,qbektrix/pyglet,Alwnikrotikz/pyglet,qbektrix/pyglet,xshotD/pyglet,Austin503/pyglet,google-code-export/pyglet,xshotD/pyglet,Austin503/pyglet,Austin503/pyglet,google-code-export/pyglet,shaileshgoogler/pyglet,odyaka341/pyglet,arifgursel/pyglet,kmonsoor/pyglet,qbektrix/pyglet,cledio66/pyglet,odyaka341/pyglet,shaileshgoogler/pyglet,gdkar/pyglet,qbektrix/pyglet,cledio66/pyglet,shaileshgoogler/pyglet,gdkar/pyglet,gdkar/pyglet,arifgursel/pyglet,xshotD/pyglet,shaileshgoogler/pyglet,xshotD/pyglet,Austin503/pyglet,kmonsoor/pyglet,google-code-export/pyglet,xshotD/pyglet,arifgursel/pyglet,Alwnikrotikz/pyglet,google-code-export/pyglet,cledio66/pyglet,odyaka341/pyglet,kmonsoor/pyglet,arifgursel/pyglet,qbektrix/pyglet,gdkar/pyglet,arifgursel/pyglet,gdkar/pyglet,kmonsoor/pyglet,odyaka341/pyglet,Alwnikrotikz/pyglet,odyaka341/pyglet,kmonsoor/pyglet,Alwnikrotikz/pyglet