Add a GtkWindowGroup struct that allows grouping together multiple windows

Add a GtkWindowGroup struct that allows grouping together multiple windows

Fri Jun  8 17:56:52 2001  Owen Taylor  <otaylor@redhat.com>

	* gtk/gtkwindow.[ch] gtk/gtkmain.c: Add a GtkWindowGroup struct
	that allows grouping together multiple windows so that grabs
	within that set of windows only affect those windows.

	* gtk/gtkmain.c gtk/gtkwidget.[ch]: Add a "grab_notify"
	signal for notification when a widget becomes shadowed
	by a grab or is no longer shadowed by a grab.

	* gtk/gtkwidget.c (gtk_widget_propagate_state)
	  gtk/gtkmain.c: (gtk_widget_grab_add): Don't allow
	insenstive widgets to maintain a grab.