Make Herald have "exists" and "not exists" options for differential reviewers on commit rules

Summary: Fixes T1485.

Test Plan: made a herald rule for "not exists". committed to master with no diff. audit was triggered

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, aran

Maniphest Tasks: T1485

Differential Revision: https://secure.phabricator.com/D6964

src/applications/herald/adapter/HeraldCommitAdapter.php

@@ -71,6 +71,13 @@ final class HeraldCommitAdapter extends HeraldAdapter {
   public function getConditionsForField($field) {
     switch ($field) {
       case self::FIELD_DIFFERENTIAL_REVIEWERS:
+        return array(
+          self::CONDITION_EXISTS,
+          self::CONDITION_NOT_EXISTS,
+          self::CONDITION_INCLUDE_ALL,
+          self::CONDITION_INCLUDE_ANY,
+          self::CONDITION_INCLUDE_NONE,
+        );
       case self::FIELD_DIFFERENTIAL_CCS:
         return array(
           self::CONDITION_INCLUDE_ALL,