To avoid visual duplication with the application menu, eliminate
the window menu button. (The window menu can still be accessed by
right-clicking on the title bar, or Alt-right-clicking anywhere on the
window.)
This is implemented using the new Mutter facility for GConf key
redirection; we add separate key for 'button_layout' with a default
that omits the menu button.
https://bugzilla.gnome.org/show_bug.cgi?id=591390
98a093a279
