Key management with tests

I have completed the key management patch with tests created by Stephen
Frost.  Original patch by Masahiko Sawada.  It requires the hex
reorganization patch first.  The key patch is now 2.1MB because of the
tests, so attaching it here seems unwise:

    https://github.com/postgres/postgres/compare/master...bmomjian:hex.diff
    https://github.com/postgres/postgres/compare/master...bmomjian:key.diff

I will add it to the commitfest.  I think we need to figure out how much
of the tests we want to add.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EnterpriseDB                             https://enterprisedb.com

  The usefulness of a cup is in its emptiness, Bruce Lee