Add support for the freedesktop.org Idle Inhibition specification,

as per:
http://people.freedesktop.org/~hadess/idle-inhibition-spec/

This makes screensaver inhibition work with GNOME 3 and other
desktop environments that implement the specification.

https://bugzilla.libsdl.org/show_bug.cgi?id=2169

--HG--
extra : rebase_source : b1967a91febdaa3f0fcb311ee1909a741722e9b2

src/video/x11/SDL_x11events.c

@@ -1029,7 +1029,19 @@ X11_SuspendScreenSaver(_THIS)
     SDL_VideoData *data = (SDL_VideoData *) _this->driverdata;
     int dummy;
     int major_version, minor_version;
+#endif /* SDL_VIDEO_DRIVER_X11_XSCRNSAVER */
 
+#if SDL_USE_LIBDBUS
+    if (SDL_dbus_screensaver_inhibit(_this)) {
+        return;
+    }
+
+    if (_this->suspend_screensaver) {
+        SDL_dbus_screensaver_tickle(_this);
+    }
+#endif
+
+#if SDL_VIDEO_DRIVER_X11_XSCRNSAVER
     if (SDL_X11_HAVE_XSS) {
         /* X11_XScreenSaverSuspend was introduced in MIT-SCREEN-SAVER 1.1 */
         if (!X11_XScreenSaverQueryExtension(data->display, &dummy, &dummy) ||
@@ -1043,12 +1055,6 @@ X11_SuspendScreenSaver(_THIS)
         X11_XResetScreenSaver(data->display);
     }
 #endif
-
-#if SDL_USE_LIBDBUS
-    if (_this->suspend_screensaver) {
-        SDL_dbus_screensaver_tickle(_this);
-    }
-#endif
 }
 
 #endif /* SDL_VIDEO_DRIVER_X11 */