BF: pyglet shaders were not respecting opacity values for image stimuli
BF: _onPygletKey was using clock.getTime

All other global timers, including what is used in _onPygletChar use
clock.getTime() (i.e. use reative to exp. start)
BF: event.Mouse.mouseMoveTime(); closes #495

- thanks to Sol for the fix
DOCS: bumped version number for release