Mouse buttons

[Fred Kiefer]

Since I did switch to XFree86 4.1.0 GNUstep does not recognize the right
mouse button of my wheel mouse (Scroll down is treated as right mouse
down). A bit of renumbering the buttons in the method [XGContext
_setupRootWindow] solved this problem. But for a general solution,
working with different X versions and mice we will have to provide a way
to configure the mouse buttons. Allowing to redefine them by the user.

I will look into this myself in a few months, if nobody finds some time
for this before. When doing so I will also try to implement scrolling
support.

Fred