Log Message:
Update sylpheed to 3.6.0

NEWS:
Changes of Sylpheed

* 3.6.0 (stable)

    * The Japanese manual was updated.

* 3.6.0beta1 (development)

    * The feature to use multiple signatures in one account was added.
    * The edit group dialog of the address book was improved to allow
      multilple selection and display its available list with folder tree.
    * The menu 'Tools - Open configuration/attachments folder' was added.
    * Printing settings and page setup are now saved.
    * The Japanese manual was updated.
    * IMAP: SUBSCRIBE command is explicitly issued for a newly created folder
      by CREATE.
    * Unix: the search location of SSL certificates for OpenBSD was added
      (#222).
    * Win32: a notice about not removing user data in the installer was
      modified.