2003-05-17  Michael Natterer  <mitch@gimp.org>

	Fixed File->Revert, which was completely broken before:

	* app/gui/file-commands.c (file_revert_confirm_callback): set the
	new image on all GimpContexts which had the old image set.  Unref
	the new image after the displays are reconnected.

	Added some paranoia code for similar future situations (the
	functions below were not broken, but affected by the above bug):

	* app/display/gimpdisplay-handlers.c (gimp_display_disconnect):
	set gdisp->gimage to NULL before unrefing the image.

	* app/widgets/gimpimagedock.c (gimp_image_dock_image_changed):
	unref the gimage pointer returned by g_object_get() only if it is
	non-NULL. Cleanup.