(Arcanist wilds) Add setHint/getHint to PhutilLockException for recent lock changes
Summary: Ref T13202. See PHI889. See D19702. A small part of that change affected libphutil, but got lost in the shuffle with all the Arcanist/wilds stuff in my local workspace.
Test Plan: See D19702.
Reviewers: amckinley
Reviewed By: amckinley
Maniphest Tasks: T13202
Differential Revision: https://secure.phabricator.com/D19720