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

[Stefan Monnier]

>> 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.


        Stefan