Make SELECT construction in PolicyAwareQuery safer

Summary: Depends on D19784. Ref T13217. Reduce uses of unsafe %Q in SELECT construction.

Test Plan: This reduces the number of safety warnings when loading Phabricator home from ~900 to ~800.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13217

Differential Revision: https://secure.phabricator.com/D19785