bug#12406: 24.2.50; frame parameter `menu-bar-lines' and `menu-bar-mode'

[Drew Adams]

> >> Because this way we'd have a consistent interface: The 
> >> presence of a frame parameter would signal "leave this
> >> frame alone".
> >
> > That's inconsistent with the convention that absence of a frame
> > parameter is equivalent to its presence with a nil value.  It is
> > similar to proposing that we give some  special signification to the
> > absense of a key in an alist, as opposed to a key with value nil.
> 
> Agreed.  That means, all frames should have a `menu-bar-lines'
> parameter, set to `default' in most of them.

Sounds reasonable.  The devil might be in the details of what you want to do
with/about it.  But yes, that sounds like a start.