Bug 677776 - filter popup windows get hidden behind main image window

On OSX, set all transient plug-in windows to UTILITY, so they appear
on top of the image window, which is a bad hack. See the comment in
gimp_window_set_transient_for_display().

libgimp/gimpui.c

@@ -260,6 +260,17 @@ gimp_window_set_transient_for_display (GtkWindow *window,
        *  where the mouse is (see bug #684003).
        */
       gtk_window_set_position (window, GTK_WIN_POS_CENTER);
+
+#ifdef GDK_WINDOWING_QUARTZ
+      /*  in OSX, bringing the plug-in's window to front hilariously
+       *  fails even though we call [NSApp activateIgnoringOtherApps];
+       *  as a workaround, set the window to UTILITY which places them
+       *  above all normal windows (which sucks, but it's better than
+       *  below the image window, and not that bad because plug-in
+       *  windows are generally temporary, see bug #677776).
+       */
+      gtk_window_set_type_hint (window, GDK_WINDOW_TYPE_HINT_UTILITY);
+#endif
     }
 }
 
@@ -283,6 +294,11 @@ gimp_window_set_transient (GtkWindow *window)
     {
       /*  see above  */
       gtk_window_set_position (window, GTK_WIN_POS_CENTER);
+
+#ifdef GDK_WINDOWING_QUARTZ
+      /*  ditto  */
+      gtk_window_set_type_hint (window, GDK_WINDOW_TYPE_HINT_UTILITY);
+#endif
     }
 }