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

On OSX, call [NSApp activateIgnoringOtherApps] when a plug-in dialog
is shown, so the plug-in process becomes the active app, and the
dialog gets focussed.

In order to avoid doing this in GimpDialog (which is also used in
the core), do it in gimp_ui_init() which all interactive plug-ins
call, and when gimp_temp_proc_run() is called interactively, to
catch repeated activation of an already running plug-in.

Also, set GimpDialog's initial position to GTK_WIN_POS_CENTER,
or they will pop up in the top left corner.

Inspired by patches from Simone Karin Lehmann and Daniel Sabo.

libgimp/gimp.c

@@ -49,7 +49,7 @@
 #define WAIT_ANY -1
 #endif
 
-#include <glib-object.h>
+#include <gtk/gtk.h> /* need GDK_WINDOWING_FOO defines */
 
 #ifndef G_OS_WIN32
 #include "libgimpbase/gimpsignal.h"
@@ -82,6 +82,10 @@
 
 #endif /* USE_POSIX_SHM */
 
+#ifdef GDK_WINDOWING_QUARTZ
+#include <Cocoa/Cocoa.h>
+#endif
+
 #if defined(G_OS_WIN32) || defined(G_WITH_CYGWIN)
 #  define STRICT
 #  define _WIN32_WINNT 0x0601
@@ -2002,7 +2006,6 @@ gimp_proc_run (GPProcRun *proc_run)
     }
 }
 
-
 static void
 gimp_temp_proc_run (GPProcRun *proc_run)
 {
@@ -2014,6 +2017,14 @@ gimp_temp_proc_run (GPProcRun *proc_run)
       GimpParam    *return_vals;
       gint          n_return_vals;
 
+#ifdef GDK_WINDOWING_QUARTZ
+      if (proc_run->params &&
+          proc_run->params[0].data.d_int32 == GIMP_RUN_INTERACTIVE)
+        {
+          [NSApp activateIgnoringOtherApps:YES];
+        }
+#endif
+
       (* run_proc) (proc_run->name,
                     proc_run->nparams,
                     (GimpParam *) proc_run->params,