Port server integration test to xvfb

[calmofthestorm]

It would be nice if we could run the server tests in xvfb for isolation from user desktop, better control of window geometry so we can test absolute mouse movements more reliably, and (wishlist) integration with CI like Travis.

I took a quick look at this today, but ran into a number of problems -- getactivewindow fails with unsupported, and key_press events were not arriving (possibly the window was not activated).