Log Message:
Update to 1.940

Upstream changes:
1.940     2017-01-29 10:33:45-05:00 America/New_York
        - no code changes since 1.939 trial release

1.939     2017-01-14 14:58:44-05:00 America/New_York (TRIAL RELEASE)
        - do not decode MIME headers known to be never encoded (Pali Roh獺r)
        - ...and that includes the Downgraded-* headers (Pali Roh獺r)

1.938     2017-01-01 20:03:38-05:00 America/New_York (TRIAL RELEASE)
        - numerous small fixes to header encoding (thanks, Pali Roh獺r)
          for more details see https://github.com/rjbs/Email-MIME/pull/32
        - When a single-part content type has been provided with multiple
          parts, the user is now warned that the type has been changed to
          multipart/mixed.  This helps catch typos like
          "mutlipart/alternative".