app: reimplement gimp_widget_flush_expose().

gimp_widget_flush_expose() has been removed since commit 3089a20167.
I now reimplemented it by simply checking if event sources are waiting
to be processed.
This was heavily needed as the statusbar was not showing any progress
(at least on highly demanding process, such as saving or loading files),
and therefore we were stuck with a seamingly frozen GUI.

Despite the name, this does not apply to a widget in particular anymore,
but to the whole program events.

app/display/gimpstatusbar.c

@@ -441,10 +441,7 @@ gimp_statusbar_progress_start (GimpProgress *progress,
           statusbar->progress_shown = TRUE;
         }
 
-#if 0
-      /* FIXME flush_expose */
-      gimp_widget_flush_expose (bar);
-#endif
+      gimp_widget_flush_expose ();
 
       gimp_statusbar_override_window_title (statusbar);
 
@@ -503,10 +500,7 @@ gimp_statusbar_progress_set_text (GimpProgress *progress,
     {
       gimp_statusbar_replace (statusbar, "progress", NULL, "%s", message);
 
-#if 0
-      /* FIXME flush_expose */
-      gimp_widget_flush_expose (bar);
-#endif
+      gimp_widget_flush_expose ();
 
       gimp_statusbar_override_window_title (statusbar);
     }
@@ -544,10 +538,7 @@ gimp_statusbar_progress_set_value (GimpProgress *progress,
               gtk_progress_bar_set_fraction (GTK_PROGRESS_BAR (bar),
                                              percentage);
 
-#if 0
-              /* FIXME flush_expose */
-              gimp_widget_flush_expose (bar);
-#endif
+              gimp_widget_flush_expose ();
             }
         }
     }
@@ -582,10 +573,7 @@ gimp_statusbar_progress_pulse (GimpProgress *progress)
 
           gtk_progress_bar_pulse (GTK_PROGRESS_BAR (bar));
 
-#if 0
-          /* FIXME flush_expose */
-          gimp_widget_flush_expose (bar);
-#endif
+          gimp_widget_flush_expose ();
         }
     }
 }

app/widgets/gimpwidgets-utils.c

@@ -1865,3 +1865,10 @@ gimp_color_profile_chooser_dialog_connect_path (GtkWidget   *dialog,
                     G_CALLBACK (connect_path_response),
                     NULL);
 }
+
+void
+gimp_widget_flush_expose (void)
+{
+  while (g_main_context_pending (NULL))
+    g_main_context_iteration (NULL, FALSE);
+}

app/widgets/gimpwidgets-utils.h

@@ -126,5 +126,7 @@ void              gimp_color_profile_chooser_dialog_connect_path
                                                     GObject               *config,
                                                     const gchar           *property_name);
 
+void              gimp_widget_flush_expose         (void);
+
 
 #endif /* __APP_GIMP_WIDGETS_UTILS_H__ */