Merge branch '6.4' into 7.0

* 6.4:
  Update lock.rst
  Add reference to undocumented configuration option

components/lock.rst

@@ -754,7 +754,7 @@ Using the above methods, a robust code would be::
  $lock->refresh();
  }
 
- // Perform the task whose duration MUST be less than 5 minutes
+ // Perform the task whose duration MUST be less than 5 seconds
  }
 
 .. caution::