oWin:Center( <oWin> ) -> NIL

------------------------------------------------------------------------------

 PARAMETER:

  <oWin>       Is the object of the window, to which our window will be 
               centered. If it is omitted the window will be centered to 
               the desktop.

 DESCRIPTION:

  Centers the window relative to another window or the screen

  EXAMPLE:

     +-------------------------------------------------------------+
     |  /* Center a Window */                                      |
     |  ACTIVATE WINDOW oWin ;                                     |
     |    ON INIT oWin:center()                                    |
     +-------------------------------------------------------------+