Log Message:
Update Courier-IMAP to 5.2.6

Changes since 4.10.0: Too many to list here (4.10.0 was released in 2011).
The full changelog can be found here:
https://sourceforge.net/p/courier/courier-libs.git/ci/b7f06ca767a6f7c03a9d24e49f659c3a23238c7a/tree/imap/ChangeLog

Note that the Maildir unicode format has changed in the 5.0 release. See
mail/courier-maildir/MESSAGE.UTF8 for details.