#63 keyset input bugs

[Bruce Sherwood]

Keyset input tested on Windows and found wanting:
f11 and f12 don't get input except for alt+f11 and alt+f12.
On actual mouse events returned by getevent() the
ctrl/alt/shift flags are set, but not on mouse status (as in
scene.mouse). Moreover, these flags once set by an
actual event are continually reported by scene.mouse
even after the keys have been released.

[Bruce Sherwood]

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Mouse flags mostly fixed on Windows by edits to wgl.cpp,
though occasionally alt doesn't seem to want to clear
appropriately when key is released. Nothing done yet about
f11 and f12.