ESC key will destroy the windows mentioned at issue 211.

This change implements generic routine gtkutil_destroy_on_esc ()
and adds invocations of it in the requisite window-handling places.

src/fe-gtk/ignoregui.c

@@ -349,6 +349,7 @@ ignore_gui_open ()
 			  mg_create_generic_tab ("IgnoreList", _(DISPLAY_NAME": Ignore list"),
 											FALSE, TRUE, close_ignore_gui_callback,
 											NULL, 600, 256, &vbox, 0);
+	gtkutil_destroy_on_esc (ignorewin);
 
 	view = ignore_treeview_new (vbox);
 	g_object_set_data (G_OBJECT (ignorewin), "view", view);