Alt should bring back menubar

[clokep]

On Windows 7/Vista, the proper behavior of having a button like this is for pressing "alt" to bring back the standard menu bar. I know this works in Firefox and there's an extension to do it as well: https://addons.mozilla.org/en-US/thunderbird/addon/4762/

[mook]

This is currently infeasible because, unlike Firefox, we don't make a new menu - we're stealing the existing one and stuffing it forcibly into a menupopup.

If we get our own menu items instead, we can look at the toolbar-menubar-autohide binding (or just use it for the main menubar).