Attach TaskPHIDs to commits in diffusion.getcommits
Summary: Uses edge query to attach TaskPHIDs to commit objects
Test Plan: Use conduit to getcommits with attached tasks
Reviewers: epriestley, Blessed Reviewers
Reviewed By: epriestley
CC: Korvin, epriestley, aran
Differential Revision: https://secure.phabricator.com/D7668