cmu/master now builds with -Werror

[Bron Gondwana]

Well, after wasting far too much of today, the 'master' branch
now builds on my machine with:

CFLAGS="-g -W -Wall -Wextra -Werror"

Unfortunately it won't build on the Jenkins server because the
ancient (seriously, imported 1997, last bugfix 2006) flex on
RHEL5 generates bogus warny code.  So I had to take that back out.

Also problems today were Cassandane not coping with the Delete
commands any more now that Cyrus nukes the offending imapd connections
which are selected to the folders which are going away.  With a more
recent perl, the $SIG{__DIE__} handler can trap them, but not with
5.8.x, so that had to be protected off as well.

Finally, I screwed up one thing which got caught - I had speculatively
changed a piece of horrible code in lmtpengine, because it looked wrong,
but it turned out the wrong was different than I had though.  Then I
committed it along with a semi-related change without looking, oops.

Cassandane + git bisect helped me find the culprit pretty fast though!

And finally, we're back.  Jenkins builds clean again.  Code cleaner,
meaning I can build locally with -Werror and be told off quicker if
I screw anything else up.

Bron.
-- 
  Bron Gondwana
  brong at fastmail.fm