Support an "authorPHIDs" constraint for "transaction.search"
Summary: Ref T13255. The "transaction.search" API method currently does not support author constraints, but this is a reasonable thing to support.
Test Plan: Queried transactions by author, hit the error cases.
Reviewed By: amckinley
Maniphest Tasks: T13255
Differential Revision: https://secure.phabricator.com/D20208