* remove includes of screen/display as Owen had them to gdk.h
* revert gdk_x11_*.grab_server changes and introduce gdk_x11_display_*.grab
* store colormap per screen in gdk_colormap_get_sytem_for_screen
* replace gdk_rgb_ditherable_for_screen() by gdk_rgb_colormap_ditherable()
* add screen property to GtkInvisible
* added idef GDK_MULTIHEAD_SAFE around gdk multihead unsafe fct
* added sanity check in gdkdisplay-x11.c and gdkscreen-x11.c