Add UDF for pg_table_is_visible

[mjgarton]

Add a UDF for the pg_table_is_visible function. This is another step towards improved pg_catalog support.

[mjgarton]

Actually I am not sure if this code is correct.

Or maybe it is correct and something else is wrong?

If I run SELECT oid FROM pg_catalog.pg_class c WHERE pg_table_is_visible(c.oid); as a quick test, pg_table_is_visible gets called with many parameters instead of being called multiple times, once for each oid.

[sunng87]

Accidently hit the merge button. Let me test it by myself later today.