[Dovecot] v2.0.18 released

http://dovecot.org/releases/2.0/dovecot-2.0.18.tar.gz http://dovecot.org/releases/2.0/dovecot-2.0.18.tar.gz.sig

    + DIGEST-MD5 authentication supports authorization id now.
      Patch by Yubao Liu
    + Added instance_name setting which is used to prefix Dovecot
      processes in ps output.
    - LDA/LMTP: Sending a large mail via submission_host or via LMTP proxy
      may have caused a hang.
    - Fixed dbox + mail_attachment_dir + zlib problems.
    - Login processes weren't logging all intended messages with
      auth_verbose=yes
    - IMAP: THREAD REFS sometimes returned invalid (0) nodes.
    - IMAP: CONTEXT search return option wasn't handled at all.
    - dbox: Various error handling fixes.
    - snarf plugin: Keep the mailbox locked during snarfing to avoid
      duplicates.