Fully legalize multiple database schemas for PostgreSQL driver

[laacz]

Hi!

Recently I ran into an issue. It is possible to supply schema config option as an array, which is an undocumented and specific feature for PostgreSQL database driver. It sets search_path, which is used when searching for schemaless objects in these schemas.

However, not everywhere this is implemented. For example, hasTable does not have this functionality.

I'd be happy to try and work on a PR. Slowly and carefully, as this would be my first contribution outside bug reports and "thumbs up".