detecting version match/mismatch between core/plugins

[Wichmann, Mats D]

Pardon a newbie question, since I don't know 
much of what's in the plans, or even that much
of what's actually implemented.

Plugins seem to be an imporant part of the design.
I'm wondering if there's a way that we can detect
if versions go out of skew.  I already stumbled
across a simple instance, when I followed the
wrong link on the plugin registry page and got
the devel version of bzrtools instead of the one
matching bzr 0.8.2 - simple operator error but
the resulting error was, er, arcane.

I guess there are three operations I can think of
off the top of my head that would interest me in 
this space:

- ask if there are newer versions of my plugins
(assuming I will only be told about ones that
are compatible with my bzr core version)

- after upgrade of core, inform me of plugins
that need to be updated for compatibility with
the new core

"bzr check-plugins" maybe for those two?

- if I invoke an incompatible plugin that I
managed to pull somehow (see above, or else,
after a core upgrade rendered one incompatible),
get a somewhat useful error about the version 
mismatch

To me this seems like maybe it should be part
of the plugin "API" such that each plugin could 
be queried for what it knows wrt. the core 
version; and for what it can't know (things in 
the future like a new version available) maybe 
consult a built-in url.

-- mats