Log Message:
Update Dovecot to 1.2.12, and Pigeonhole Sieve to 0.1.17.

ChangeLog for Dovecot 1.2.12:

- deliver: Don't crash when a message with Auto-submitted: header gets
  rejected.
- lib-storage: Fixed header searches to work correctly when there are
  multiple headers with same name.
- dict client: Disconnect from dict server after 1 second of idling.
- dict: If process crashed, it wasn't automatically restarted
- dict file: If dict file's group permissions equal world permissions,
  don't try to change its gid.
- maildir: Fixed a memory leak when copying with hardlinks.
- maildir: Expunging last messages may have assert-crashed if their
  filenames had just changed.

Changelog for Sieve 0.1.17:

- Made sure source code positions for compiler messages are recorded
  at start of tokens.
- Fixed a few potential memory leaks in the Sieve compiler and the
  spam/virustest extensions.
- Made command line tools return proper exit status upon failure.