bug#6491: 24.0.50; list-buffers should not throw away marks

[Drew Adams <drew.adams@oracle.com>]

> > Docstring ""v runs the command Buffer-menu-select (found in
> > Buffer-menu-mode-map),""
> > doesn't even mention it throws away the marks.
> 
> No, but it's common (in some modes)

Which ones?  Maybe they should change, to take
advantage of the other (superior ;-)) behavior.

Do they have a notion of updating - does `g'
update them in some way?  Or does it just reset
them?

A file listing is a perfect case for having `g'
update - sync with the world outside the buffer
state.  That you can do that but keep other
aspects of the buffer state is a plus.

Maybe the modes you have in mind do not have
any notion of updating, so `g' just does a
total reset?  If not, they might be candidates
for upgrading to the Dired-like behavior. ;-)

> to first mark a bunch of stuff, and
> then when you execute the command on those marked things, the marks are
> cleared so that you can then mark some other things and do some stuff
> on them.

That's only useful when it's necessary because
no one provided an alternative.  And it's only
necessary if the mode doesn't have a simple
way to clear the marks on demand.  (`M-DEL RET'
in Dired.)

Separating clearing marks from syncing the buffer
is a plus.  There's no good reason to hard-couple
the two - unless reverting does no updating, i.e.,
unless it's essentially just clearing marks.

> Dired is one mode that doesn't work like that, but it's not the only
> mode in Emacs.

It's not the only one, but it's a good one.  And
it's clearly the closest one to the behavior of
`list-buffers'.