Modernize metamta.differential.patch-format

Summary: Change metamta.differential.patch-format over to an enum option now that they're implemented.

Test Plan: Looked at settings page.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D16032

src/applications/differential/config/PhabricatorDifferentialConfigOptions.php

@@ -261,13 +261,14 @@ final class PhabricatorDifferentialConfigOptions
             "that many lines. For instance, a value of 100 means 'inline ".
             "patches if they are no longer than 100 lines'. By default, ".
             "patches are not inlined.")),
-      // TODO: Implement 'enum'? Options are 'unified' or 'git'.
       $this->newOption(
         'metamta.differential.patch-format',
-        'string',
+        'enum',
         'unified')
         ->setDescription(
-          pht("Format for inlined or attached patches: 'git' or 'unified'.")),
+          pht('Format for inlined or attached patches.'))
+        ->setEnumOptions(
+          array('unified' => 'unified', 'git' => 'git')),
     );
   }