In case of GConf failure, fall back to local keybinding values

Always compile the default keybindings into Metacity, and if we
fail to retrieve the values from GConf, use the compiled-in
value. This makes things more robust especially in an environment
like JHBuild where GConf-schema-installation may not work
correctly.

Also use these values for the no-GConf case, rather than
having a separate arrray and code path.

http://bugzilla.gnome.org/show_bug.cgi?id=576127

src/include/prefs.h

@@ -222,6 +222,7 @@ typedef struct
 typedef struct
 {
   const char   *name;
+  const char   *default_keybinding;
   /**
    * A list of MetaKeyCombos. Each of them is bound to
    * this keypref. If one has keysym==modifiers==0, it is