Add support for GTK dockapps.
Quoting anomie from wmudmount's bug tracker:
"Back in 2010, WindowMaker implemented a system where windows with WM_CLASS res_class = DockApp would be treated as if they had initial_state = WithdrawnState, since GTK refuses to allow this."
please try the attached patch and see if you like it.
Thank you. Seems to work now.