wmaker: add support for more mouse buttons

This patch is adding support for back/forward mouse buttons
and the left/right wheel tilt buttons.

src/keybind.h

@@ -2,6 +2,7 @@
  *  Window Maker window manager
  *
  *  Copyright (c) 1997-2003 Alfredo K. Kojima
+ *  Copyright (c) 2014 Window Maker Team
  *
  *  This program is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
@@ -21,6 +22,23 @@
 #ifndef WMKEYBIND_H
 #define WMKEYBIND_H
 
+/* <X11/X.h> doesn't define these, even though XFree supports them */
+#ifndef Button6
+#define Button6 6
+#endif
+
+#ifndef Button7
+#define Button7 7
+#endif
+
+#ifndef Button8
+#define Button8 8
+#endif
+
+#ifndef Button9
+#define Button9 9
+#endif
+
 enum {
 	/* anywhere */
 	WKBD_ROOTMENU,