This widget is derived from the XmMANAGER class, and thus inherits all this class' resources.
It enables GPHIGS to be completely integrated into the Motif toolkit, and authorises access to all GPHIGS-GUI functions. It may manage a scrolled window, links between scrollbars, etc....
NB : When the widget is created, the workstation does not need to be opened (popen_ws), the widget itself is responsible for this opening.
