oracle use NULLS first
oracle use NULLS first

the order of nulls relative to columns with values is setup as
a default value in databases, which can be changed. The default for
postgres is to have nulls last. Looks like oracle has the same.

This PR has oracle enhanced driver follow suite as postgres.

Postgres and rails 6.0 and earlier had issues with the null first, so this is
feature limited to 6.1 and later

stefankroes/ancestry,kbrock/ancestry