Update cyrus-imapd24 to 2.4.15.

Changes to the Cyrus IMAP Server since 2.4.15

      * Bug #3651 - 64 bit dirhash breaks existing systems. NOTE this
        includes a fix to the re-written rehash tool released with 2.4.15

Changes to the Cyrus IMAP Server since 2.4.14

      * Bug #3664, #3665 - Sieve filters don't work if mailbox contains
        dots
      * Bug #3651 - 64 bit dirhash breaks existing systems. NOTE - this
        includes a complete rewrite of tools/rehash, making it much simpler
        and more reliable. Check the usage statement
      * Bug #1228 - mailbox dumps need to dump quotaroots
      * Bug #3613 - CATENATE command returns BADURL
      * Bug #3627 - enabling improved_mboxlist_sort documentation mention
        subscription files
      * Bug #3661 - Memory leaks in sync_server, nntpd, popd
      * Bug #3621 - quota bug involving nested quota roots
      * Bug #3667 - FLAGS.SILENT needs to return new MODSEQ if QRESYNC
        enabled

(obache)