[MariaDB Packagers] MariaDB 5.5.64 release prep

Prep work for the MariaDB 5.5.64 release has begun. Expected release date is Mon, 29 Apr 2019. Draft release notes and changelog: - https://mariadb.com/kb/en/mdb-5564-rn/ - https://mariadb.com/kb/en/mdb-5564-cl/ As usual, the release notes and changelog are still in draft form at this time and will be updated prior to release. Thanks. -- Daniel Bartholomew, MariaDB Release Manager MariaDB | https://mariadb.com