Patch fixes the default value of the WM_CLASS property of a newly created
window. It sets it to the WM_CLASS of the invisible leader instead of
NULL:NULL which may be disastrous for session-managing windowmanagers
(for example WindowMaker).

This patch *should* definitely go into 1.0.

Testet with the test-apps and The GIMP.

Comments to Oliver Graf <ograf@fga.de>.