Fix an old header encoding buglet in mailer.py.

* tools/hook-scripts/mailer/mailer.py
  (MailedOutput._rfc2047_encode): New function.
  (MailedOutput.mail_headers): Use _rfc2047_encode() to properly
    encode the From:, To:, and Subject: headers

Patch by: Igor Galić <i.galic@brainsware.org>
          (Scope expanded by me.)


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1487532 13f79535-47bb-0310-9956-ffa450edef68