The expose-event/draw signals were used to reenable the menu
after it has been disabled when VTE overrides the given keybinding.
This doesn't work on OS X where GtkMenuBar isn't displayed
(there may be a similar problem with the global menubar on
Ubuntu).

The reason why these signals were used was probably slight
flickering of the menubar when using ordinary g_idle_add() to
reenable the menu (the dimmed menu gets drawn after which
it gets reenabled and redrawn non-dimmed). It is however possible
to use idle function with higher than redraw priority in which case
the menu is enabled before the redraw so the dimmed menu
isn't drawn at all.

Fixes https://sourceforge.net/p/geany/bugs/1081/