minor freeze break request: _GNOME_WM_KEYBINDINGS property

[Owen Taylor <otaylor redhat com>]

[ Please CC me on replies, I'm not on gnomecc-list ]

I'd like to get:

 http://bugzilla.gnome.org/show_bug.cgi?id=594067

Into gnome-control-center for 2.28.

What it basically is about is allowing the GNOME Keybindings capplet to
show the shared Metacity/Mutter keybindings when Mutter is running
without having Mutter have to pretend to be Metacity.

(Pretending to be Metacity would cause other problems; in particular it
would be very hard to write a robust tool to switch from Metacity to
Mutter, since it wouldn't know when the new window manager started.)

This should be a very safe change; unless I did something stupid in the
patch, I see zero chance of affecting users negatively. There are no
string or UI changes.

- Owen