accel should be _accel in UI XML files

[Darin Adler <darin eazel com>]

Keyboard accelerators have to be translated along with the wording of menu
item. Some of them might stay the same, but some might have to change.

So we should change "accel" to "_accel" in Bonobo UI XML files. There's no
big hurry to make this change, but if we don't I think we'll regret it.

The downside of this is that due to the way the gettext framework works, you
have to change all accelerators that use the same key combination en masse.
So maybe it's not a good idea.

Thoughts?

    -- Darin