Log Message:
Update sylpheed to 0.9.1, main changes are:

    * The bug in handling folder names which include '+' in IMAP4
      modified UTF-7 conversion has been fixed.
    * The wrong parsing of message/rfc822 parts in multipart messages
      has been fixed.
    * Several bugs of auto signature replacement has been fixed.
    * A bug that didn't hide user string in the Action dialog has been
      fixed.
    * Socket I/O timeout interval is now configurable.