(rfc) recommend installing a plugin when needed

[Martin Pool]

Mark mentioned this morning the success Ubuntu has had with
automatically suggesting packages that need to be installed.  By
default, Ubuntu installs a fairly selective set of packages for the
desktop or server, so that it fits on one CD and does not ask
questions about packages during installation.  But if you later type a
command in bash that depends on a missing package, it tells you how to
install it.  (I personally rarely see this because I use zsh but
anyhow.)  Something similar is done for media files, other file
types(?) and web content.

So I wonder if we could, or should, do this for Bazaar.  If someone
types 'bzr shelve' we can suggest bzrtools, gannotate for bzr-gtk and
so on.  This could be as simple as registering stub commands or help
topics for the most important plugin commands.

Obviously there are some things plugins can do, like providing hooks,
or new options on existing commands, that aren't covered here.  And if
they really are commonly used, maybe they should just be moved into
the core, or into shipped plugins, or pulled in by the packaging
system.

This makes more sense if we have an install-plugin command
<https://bugs.launchpad.net/bzr/+bug/81393> or something similar, but
is useful anyhow.

-- 
Martin