ClrScr procedure

  DECLARATION:  ClrScr

      PURPOSE:  Clears the current window and homes the cursor.

         UNIT:  CRT

      REMARKS:  All characters are set to blanks using the current
                color attribute set with TextBackground.  The cursor is
                positioned in the upper left corner of the active window.

                This procedure is Window Relative in that area cleared will
                not extend outside a current window.