Change to new official postgresql.org apt repo and support version 9.3

Change postgres apt repo to the one specified at http://wiki.postgresql.org/wiki/Apt

According to the [changelog](http://upstream-tracker.org/changelogs/postgresql/9.3beta2/changelog.html) under server settings, postgresql 9.3 changed unix_socket_directory to unix_socket_directories. This change accounts for that.

I have not extensively tested all features of the crate to ensure no regressions.