bug#7303: Suggestion: Move minor mode menus to one common top-levelsubmenu

[Drew Adams]

> I suggest we move all minor mode to one common top-level submenu for
> two reasons:
> 
> - It takes less space in the menu bar.
> - The distinction between minor and major modes becomes more clear.
> 
> This submenu could also preferably be ordered by local and 
> global minor modes.

IMO, that's not the right solution.

We should leave it up to users and libraries to decide where to put menus.  This
kind of choice depends on the context, and sometimes on user preference.  The
devil is in the details.

However, some general mechanism to deal with an overly wide menu bar or mode
line could be useful, especially if optional.

Currently, the menu bar and mode line are treated differently when their content
is too wide for the frame and window, respectively. The menu bar content is
wrapped. The mode line content is truncated at the right.

* This might be useful for the mode line:

Whenever stuff cannot be displayed and will be truncated, gather it and make it
all accessible by a link in the mode line.  Obviously, the link itself takes
some space, but it could be short (e.g. `...').

* Something similar would be helpful for the menu bar:

Have a user option that specifies a max width. If nil, then the current behavior
would be followed (just wrap).  Otherwise, if the menu-bar content is wider than
the option value, then the behavior would be similar to the mode-line behavior
suggested above: Gather all menus that would be wrapped into a final menu `...'
instead.