Fix for PHP spewing notices from commit a373d07ae0

Please test with error_reporting set to E_ALL!

Classnames and function names aren't first-class objects in PHP and need to be referenced as strings here. :(

plugins/UserFlag/UserFlagPlugin.php

@@ -48,7 +48,7 @@ class UserFlagPlugin extends Plugin
         $schema = Schema::get();
 
         // For storing user-submitted flags on profiles
-        $schema->ensureDataObject(User_flag_profile);
+        $schema->ensureDataObject('User_flag_profile');
 
         return true;
     }