Issue 611: fix sign of mouse dy so that up is positive and down is negative
Issue 611: fix sign of mouse dy so that up is positive and down is negative

oktayacikalin/pyglet,oktayacikalin/pyglet,oktayacikalin/pyglet,theblacklion/pyglet,oktayacikalin/pyglet,theblacklion/pyglet,theblacklion/pyglet,theblacklion/pyglet,theblacklion/pyglet,oktayacikalin/pyglet