Use sort, not text, for search index table

Summary: Ref T1191. The index's case sensitivity depends on the column type. Using `text` makes the search case-sensitive, which is not desirable.

Test Plan: After adjustment, searched for "PROJECTS" and found hits against "projects".

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T1191

Differential Revision: https://secure.phabricator.com/D10619

src/applications/search/storage/document/PhabricatorSearchDocumentField.php

@@ -15,7 +15,7 @@ final class PhabricatorSearchDocumentField extends PhabricatorSearchDAO {
         'phidType' => 'text4',
         'field' => 'text4',
         'auxPHID' => 'phid?',
-        'corpus' => 'text?',
+        'corpus' => 'sort?',
       ),
       self::CONFIG_KEY_SCHEMA => array(
         'key_phid' => null,