gdk/x11: Add gdk_x11_device_manager_lookup()

This function can be used to find the GdkDevice wrapping
an XInput2 device ID. For core devices, the Virtual Core
Pointer/Keyboard IDs (2/3) may be used.

gdk/x11/gdkx11devicemanager.h

@@ -0,0 +1,39 @@
+/* GDK - The GIMP Drawing Kit
+ * Copyright (C) 2011 Carlos Garnacho
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+#if !defined (__GDKX_H_INSIDE__) && !defined (GDK_COMPILATION)
+#error "Only <gdk/gdkx.h> can be included directly."
+#endif
+
+#ifndef __GDK_X11_DEVICE_MANAGER_H__
+#define __GDK_X11_DEVICE_MANAGER_H__
+
+#include <gdk/gdk.h>
+
+#include <X11/Xlib.h>
+#include <X11/Xutil.h>
+
+G_BEGIN_DECLS
+
+GdkDevice * gdk_x11_device_manager_lookup (GdkDeviceManager *device_manager,
+                                           gint              device_id);
+
+G_END_DECLS
+
+#endif /* __GDK_X11_DEVICE_MANAGER_H__ */