DelLine procedure

  DECLARATION:  DelLine

      PURPOSE:  Deletes the line containing the cursor

         UNIT:  CRT

      REMARKS:  The line containing the current cursor position is deleted.
                All lines below the deleted line are scrolled up and a new
                line is added to the bottom.  The scrolling is done with the
                BIOS scroll routine.

                All of the characters in the new line, inserted at the bottom,
                are set to blanks using the currently defined text attributes.
                If TextBackground is not set to black, the new line will be
                created in the defined background color.

                This procedure is Window Relative in that the deleted line
                will not extend outside a current window.