[Checkers] Checker for JCIP @GuardedBy annotation

[Michael Ernst]

Jeremy-

> I don't actually have any projects with it either.  I think there is
> something of a chicken-egg problem here, which is that without the
> checker, people don't actually find it useful to put in the
> annotations.

You're exactly right here.  Hopefully the existence of a checker will break
the impasse.

I should note that FindBugs does some partial checking of @GuardedBy,
though a web search indicates some problems with its implementation.

> Now that there is a checker, I will ask around a bit and
> see if someone wants to use it in their project.

Great, we appreciate it.  We can try it on some random open-source
software, but a case study is *much* more effective when someone who knows
and cares about the code is helping out.  And, the case study should help
the developers too.

Thanks!

                    -Mike