Index users in search results.

Summary:
Add users to the search results. I need to follow this up with a patch to make
the search results stop being terrible. I'll do that.

Test Plan:
Searched for users, ran "reindex_all_users.php"

Reviewed By: jungejason
Reviewers: tomo, jungejason, aran
CC: aran, jungejason
Differential Revision: 508

src/__phutil_library_map__.php

@@ -493,6 +493,7 @@ phutil_register_library_map(array(
     'PhabricatorSearchQuery' => 'applications/search/storage/query',
     'PhabricatorSearchRelationship' => 'applications/search/constants/relationship',
     'PhabricatorSearchSelectController' => 'applications/search/controller/select',
+    'PhabricatorSearchUserIndexer' => 'applications/search/index/indexer/user',
     'PhabricatorSetup' => 'infrastructure/setup',
     'PhabricatorStandardPageView' => 'view/page/standard',
     'PhabricatorStatusController' => 'applications/status/base',
@@ -951,6 +952,7 @@ phutil_register_library_map(array(
     'PhabricatorSearchMySQLExecutor' => 'PhabricatorSearchExecutor',
     'PhabricatorSearchQuery' => 'PhabricatorSearchDAO',
     'PhabricatorSearchSelectController' => 'PhabricatorSearchController',
+    'PhabricatorSearchUserIndexer' => 'PhabricatorSearchDocumentIndexer',
     'PhabricatorStandardPageView' => 'AphrontPageView',
     'PhabricatorStatusController' => 'PhabricatorController',
     'PhabricatorTaskmasterDaemon' => 'PhabricatorDaemon',