FYI, more fine grained locking

[Sebastian Spaeth]

Hi all, I won't be sending in the patch this late in the release series,
but in order to prevent duplication of coding I want to announce that I
have a more fine-grained locking ready that I will sens as soon as we
start a new unstable series after the next release.

It implements a per-account lock and not a global lock, that is you can
invoke offlineimap hourly in cron to sync one account and still invoke
offlineimap manually to sync another. There is also a debian bug about
this somewhere.

The change was relatively easy to make. Or is this something that we
want in this round still?

The patch is 2 files 40+ 20- (it is larger because we do proper lock
file removal at the end, rather than just always leaving the file exist
as we do now).

Sebastian