Comment 8 for bug 1031535

Worked for me in testing, and the code (while pretty dense overall) eventually made sense to me. Since a LEFT JOIN is effectively the same as an INNER JOIN if we have a non-null WHERE condition on the table being joined anyway, I couldn't think of a case where changing to a LEFT JOIN would actually hurt this interface.

Pushed to master, rel_2_4, and rel_2_3. Thanks, all!