Add magic formula to keep DB_DataObject from treating location prefs pkey as autoincrement

classes/User_location_prefs.php

@@ -45,4 +45,9 @@ class User_location_prefs extends Memcached_DataObject
 
     /* the code above is auto generated do not remove the tag below */
     ###END_AUTOCODE
+
+    function sequenceKey()
+    {
+        return array(false, false, false);
+    }
 }