NSMenu reorganisation

[Fred Kiefer]

When we switch a menu between horizontal and vertical mode we reorganize
a few menu items. A similar reorganisation happens when we load a NIB
file for a menu. I just commited a change that tries to bring these two
implementations together. For now I just changed the code in NSMenu, the
duplication for the NIB loading is still intact. I would like to ask all
of you who are interested in this subject to try and inspect the new
code and if nobody complains I will remove the special NIB loading code
for menus.

Fred