PE-1648 - Initial support of NATURAL JOINs.
PE-1648 - NATURAL JOINS rewrite using USING() clause.
PE-1648 - Intermediate commit.
Merge branch 'master' of git@github.com:Tesora/tesora-dve-pub.git into pe1648
PE-1648 - Rewrite NATURAL [LEFT] JOIN of two tables as an INNER JOIN or
a LEFT JOIN with a USING clause that names all columns that exist in
both tables. The rewrite takes place before other join transformations.
PE-1648 - Fix unit test.
Merge branch 'master' of git@github.com:Tesora/tesora-dve-pub.git into pe1648