Fix an issue with "Auditors:" where an edge edit was used as a PHID list
See https://discourse.phabricator-community.org/t/runtimeexception-during-import-of-commit/3801. When importing commits with "Auditors:", a raw transaction new value (with an edge edit map using a "+" key) may be passed as an unmentionable PHID list.
Instead, pass an actual PHID list.
- Pushed a commit with "Auditors: duck".
- Ran daemons.
- Before patch: umentionable PHID exception.
- After patch: clean commit import.
- Verified "duck" was added as an auditor.
Differential Revision: https://secure.phabricator.com/D21181