send_pointer
Description:
Move the remote pointer to position (x, y) and set the button state to button_mask.
This method will only work if the desktop is using absolute pointer mode. It will be a no-op if in relative pointer mode.
Parameters:
| this | 
           the VNC display widget  | 
      
| x | 
           the desired horizontal position  | 
      
| y | 
           the desired vertical position  | 
      
| button_mask | 
           the state of the buttons  |