Log Message:
Update to 6.8

Changelog:
* Mew now supports Emacs 24.3 or later only.
* Supporting stunnel 5.
* Supporting GnuPG 2.1.23 or later.
  The command name should be "gpg" instead of "gpg2".
  Put the following to your "~/.gnupg/gpg.conf".
        no-auto-key-retrieve
        auto-key-locate local
* Using LibreOffice (soffice) on Unix by default