Various Postgres fixes (bug 26612 stuff)

Various Postgres fixes (bug 26612 stuff)
* Remove last of $wgDBuser-specific settings like timezone, datestyle and search_path. This is all handled by open() :D
* Only set search_path if the schema exists (rather than just set to some random string), fall back to 'public' otherwise
* Only call setupUser() if we need to _CreateDBAccount, otherwise it returns immediately and confuses you (no functional change)
* Implement selectDB() for Postgres, basically call open() with a new DB name
* Try to fix setupDatabase() for this "user must be owner of relation" error I'm getting when the $wgDBuser exists (have tried with roles granted && no roles granted). I get no errors at all when