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Summary: See PHI1048. We have similar transactions elsewhere already (particularly, on tasks) and these edges don't have any special properties (like "Closes Txx As Wontfix" edges do) so this doesn't create any sort of peril.

Test Plan: {F6170556}

Reviewers: amckinley

Reviewed By: amckinley

Differential Revision: https://secure.phabricator.com/D20075