Error Message

[Martin Pool]

> The combination of "system crash at the wrong moment" and "on certain
> systems" is probably about as rare as reports of this problem, so therefore I
> must be right ;)

This is a similar situation to <https://bugs.launchpad.net/bzr/+bug/185103>.

We should at least try to print it properly as, maybe "lock with no
info file" and recommend breaking it.

I'm wondering if we should flush the file after writing it.  That
doesn't guarantee it will survive, and we but it might improve the
odds.  syncing even a single file can be slow (?), butwe should be
taking locks only a few times per invocation.

-- 
Martin