Improve memory usage by allocating the sprite's memory only to devices that
actually have a sprite and provide means to remove a device's cursor from the
screen (more hotplugging, yay!).
This commit breaks ScreenRec's ABI.
of errors.
Some copyright notices.
misprite.c passes DeviceIntPtr around and down to DC (previously
miCursorInfoPtr and the plain device id).
Large cleanup in misprite.c to avoid code duplication.
