Log Message:
Update to Dovecot 1.1beta16, and bump the API_DEPENDS version to it.

>From the release announcement mail:

If all goes well, I'll release v1.1.rc1 in a couple of days. Now's a good time
to start testing v1.1 :)

Changes since beta15:

 - Squat is finally working and supports expunging messages from it.  I've been
   stress testing it and can't find any problems anymore.
 - Some index/cache crashfixes

TODO for v1.1.0:

 - mbox: We write From_-lines to message bodies unescaped and assume
   Content-Length: header allows us to skip over them. This probably worked in
   v0.99, but got broken when mbox code was rewritten for v1.0. This should be
   fixed somehow.
 - dbox: fsync()ing isn't done for saved messages.
 - maildir: after rename()ing files from tmp/ to new/ we should probably
   fsync() the new/ directory.
 - Squat: NFS support. Check/fix a potential locking problem.
 - Lucene: It gives all kinds of locking errors which cause other problems.
   Maybe Dovecot should do the locking itself so Lucene never needs to wait for
   locks? Has anyone here used Lucene before and knows about these issues?