Add %LJ (joined with spaces) to qsprintf() for merging JOIN clauses

Summary: Depends on D19783. Ref T13217. Beyond AND, OR, and comma, we also need spaces to join JOIN clauses. Add %LJ, like the other query sublist conversions.

Test Plan: See upcoming changes.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13217

Differential Revision: https://secure.phabricator.com/D19786