Update the EPLA packaging key (previous key expires 2019-09-23)

Update the EPLA packaging key (previous key expires 2019-09-23)

Add the new upstream key from this upstream commit:

  commit f16785d361097df9fddfcc0b60ae6f0d92e7e911
  Author: Stefan Monnier <monnier@iro.umontreal.ca>
  Date:   Wed May 8 13:19:36 2019 -0400

    * etc/package-keyring.gpg: Add the 2019 key (backport)

    Origin: backport, commit: 916510b6d919a333d1dac528a9d051aa6d857ccc
    Forwarded: not-needed

Add the old and new keyrings to debian/ and
debian/source/include-binaries since debian/patches/ can't handle git
binary diffs.

Thanks to Stefan Monnier for reporting the problem and providing the
patch.