lock_sync
Description:
Locks a resource identified by uri, or, in case it's null, on the URI defined in associated 
      Source.
The out_lock_token can be refreshed with 
        refresh_lock_sync. Release the lock with unlock_sync.
      Free the returned out_lock_token with g_free, when no longer needed.
If provided, free the returned out_xml_response with xmlFreeDoc, when no longer needed.
Parameters:
| this | |
| uri | 
           URI to lock, or   | 
      
| depth | 
           requested depth, can be one of WEBDAV_DEPTH_THIS or WEBDAV_DEPTH_INFINITY  | 
      
| lock_timeout | 
           timeout for the lock, in seconds, on 0 to infinity  | 
      
| xml | 
           an XML describing the lock request, with DAV:lockinfo root element  | 
      
| out_lock_token | 
           return location of the obtained or refreshed lock token  | 
      
| out_xml_response | 
           optional return location for the server response as   | 
      
| cancellable | 
           optional Cancellable object, or   | 
      
Returns:
| 
           Whether succeeded.  |