Changes:

- docker-library/postgres@03e7695: Merge pull request docker-library/postgres#801 from infosiftr/db-exists
- docker-library/postgres@eaeb73d: Merge pull request docker-library/postgres#804 from infosiftr/chmod-no-fail
- docker-library/postgres@36ffea2: Adjust "chmod" to not fail (since PostgreSQL validates this itself later)
- docker-library/postgres@11e397d: Do not try to create databases that already exist
- docker-library/postgres@3690694: Merge pull request docker-library/postgres#797 from infosiftr/rc-beta-alpha
- docker-library/postgres@dba8ec0: Adjust tagging to enforce explicit pre-release opt-in