plugins: Add GTK3 support

plugins/docinfo/pluma-docinfo-plugin.c

@@ -72,7 +72,11 @@ static void docinfo_dialog_response_cb (GtkDialog   *widget,
 					PlumaWindow *window);
 
 static void
+#if GTK_CHECK_VERSION (3, 0, 0)
+docinfo_dialog_dispose_cb (GObject  *obj,
+#else
 docinfo_dialog_destroy_cb (GtkObject  *obj,
+#endif
 			   WindowData *data)
 {
 	pluma_debug (DEBUG_PLUGINS);
@@ -142,8 +146,13 @@ get_docinfo_dialog (PlumaWindow *window,
 				      GTK_WINDOW (window));
 	
 	g_signal_connect (dialog->dialog,
+#if GTK_CHECK_VERSION (3, 0, 0)
+			  "dispose",
+			  G_CALLBACK (docinfo_dialog_dispose_cb),
+#else
 			  "destroy",
 			  G_CALLBACK (docinfo_dialog_destroy_cb),
+#endif
 			  data);
 	g_signal_connect (dialog->dialog,
 			  "response",