RegisterBGIfont function

  DECLARATION:  RegisterBGIfont(Font : Pointer) : Integer

      PURPOSE:  Registers a user-loaded or linked-in BGI font with the
                graphics system.

         UNIT:  Graph

  RESULT TYPE:  Integer

      REMARKS:  With this, a user may load a font file and 'register'
                it by passing its memory location to RegisterBGIfont.
                When that font is selected by calling SetTextStyle, the
                registered font will be used instead of being loading from
                disk by the Graph unit.

                If an error occurs, the returned value is less than zero,
                otherwise the internal font number is returned.