Manual merge with upstream as of 2017-07-25

[mcd-php]

Failed with proper merge attempt, started from docker-library/postgres and manually picked changes from DanielDent/docker-postgres-replication.

[DanielDent]

Thanks for this work a while back - I apologize I was not able to provide better feedback as to why I hadn't merged it.

I've created a new patch based build process on the dev branch, and builds from this process temporarily live at https://hub.docker.com/r/danieldent/docker-postgres-replication-dev/ until I and other community members have had a chance to test these updates (the new build process also builds the -alpine variants as well as Postgres 10). I have not had time to even run these new builds, so please run this builds in test prior to dropping them into a production environment.