- The environment variables PGUSER and PGDATABASE are used instead of
   POSTGRES_USER and POSTGRES_DB.  This is so that those environment variables
   can be defined in a docker-compose.yml file for the database container and
   then be inherited by other services that need to connect to the database so
   that they can just define PGHOST to the name of the database container and
   then use 'psql' without any connection parameters.
 - pg_hba.conf is changed to restrict external access to the database to
   'samenet' instead of 'all'.  This makes it so that other containers in the
   deployment can connect to it, but other external addresses are not able to.
 - [pgcli](http://pgcli.com/) is installed as an alternative to the built-in
   `psql` command. (Only in the debian-based images)
 - The suggestions for postgresql.conf taken from Christophe Pettus's excellent
   talk at https://www.youtube.com/watch?v=jqmdujimzfq are included.

to use the database that hasn't been created yet.

directories.

 - Allow the checkpoint_timeout to be configurable by setting the
   CHECKPOINT_TIMEOUT environment variable when the database is
   created.
 - Rotate logs more effectively by keeping a week's worth of logs and
   naming the log files with the day of the week in them.

See https://github.com/tbeadle/docker-barman for an image to be used as
the barman server.