stop fullscreen windows from stealing focus

A fullscreen window steals next focus when the currently focused window is:
* Minimized (normal minimize or by show desktop)
* Closed by any method
* Hidden (closed to system tray for example)

This pull addresses the issue by removing META_LAYER_FULLSCREEN.  I'm proposing this as a replacement for pull #127.  I've tested this patch with VLC player fullscreen on monitor 2.  I used audacious with the system tray plugin to test a hidden window, I used gedit for minimize and close tests.