[MERGE] Implement reconfigure --standalone and --sharing

[Eric Siegerman]

Way back at the beginning of this thread, Aaron Bentley wrote:
> This patch allows reconfigure to convert a branch to be standalone, or
> to use a shared repository.

Thanks so much, Aaron.  This'll eliminate a (to me, at least) major
annoyance.

> I've termed a branch-that-uses-a-shared-repository a "sharing"
> branch [...]

How how about calling them "lightweight branches", by rough
analogy with "lightweight checkouts"?  The unifying concept is
that neither one is standalone; each is totally dependent on some
external directory tree to do its job.

(Sure, a heavy-weight checkout is intended to interact with an
external branch; but it isn't totally dependent on the latter, as
a lightweight checkout is -- or as a lightweight branch is on its
(external) shared repository.  So the analogy isn't too far off,
IMO.)

 - Eric