[RP] handling transient windows

[shawn]

Just in case you were wondering I've add some code to handle transient
windows a little nicer. A while back they started appearing as the
only window visible. Now when you switch to a transient its
transient_for (parent) window is also mapped. If it is a transient
window it maps its transient_for, and so on until the transient_for
window is not a transient window. They are still centered. The only
thing left to do is fix up some unneeded window repainting...