Allow get_tables to see views and v10-style partitioned tables

[coreyhuinker]

And it does so with just one query.

[arikfr]

Is this backward compatible?

[coreyhuinker]

tl;dr - yes

The catalog tables (pg_class, pg_attribute, pg_namespace) are present in all supported version of postgresql (and have probably been there since postgres started).

There have been no instances of postgres changing a relkind value from version to version, and it would be a major upgrade headache if they did try doing that.

While partitions don't exist prior to v10, there's no harm in running a query that would not filter out the nonexistent rows.

We may have to tweak the IN clause when new discoverable object types are made available in future version of postgres, but that's about it.

That, and the existing code risked duplicate entries for mviews if a future version of information_schema decided that mviews were tables.

This query should also work for the postgresql forks (Vertica, Redshift) though they may have chosen different relkind values for the object types.

[arikfr]

Thank you for the pull request and the detailed explanation!