postgresql: Improve and cleanup module.

Essentially why I'm doing a pull request instead of directly pushing here is because of a6c2e79af979530769e0727bf51a735e3f3f1297, which could break configurations out there.

At the current master `enableTCPIP` has no effect at all, because of the reason I described in the mentioned commit.

So, with this commit, it will essentially break configurations where users have just ignored `enableTCPIP`, which leads to PostgreSQL listening to local TCP/IP connections by default (which I presume wasn't intended, because `enableTCPIP` defaults to `false`).

Which brings me to the main question: Should we enable listening to local TCP/IP connections by default?