VC command for showing outgoing changes

[Dan Nicolaescu]

It would be nice to have a VC command for showing the outgoing changes
for distributed VC systems (i.e. the log of the changes that will be
pushed when you do a VC push).
Let's call this method vc-outgoing (name suggestions are welcome).

vc-hg-outgoing does this, but it's only for mercurial, it would be good
to have a generic method for doing such a thing.

vc-print-log uses modes derived from log-view-mode.  

vc-outgoing cannot quite use that because most commands that are defined
for log-view-mode do not make sense (annotate, next/previous file, show
version).

Some commands that would make sense for vc-outgoing: show the diff,
push, create a bundle, send by email.

One thing we can do is to create a log-view-base-mode and have
log-view-mode and log-view-outgoing-mode derive from this mode, and have
log-view-mode and log-view-outgoing-mode define their own commands and
key bindings.

Something similar can be done for incoming changes.

Ideas, opinions, suggestions etc are welcome (code would be even better).