Fix issue 95: OS X mouse drag outside window.
Fix issue 95: OS X mouse drag outside window.

adamlwgriffiths/Pyglet,niklaskorz/pyglet,niklaskorz/pyglet,niklaskorz/pyglet,seeminglee/pyglet64,seeminglee/pyglet64,niklaskorz/pyglet,adamlwgriffiths/Pyglet,adamlwgriffiths/Pyglet,seeminglee/pyglet64,adamlwgriffiths/Pyglet