Close procedure

  DECLARATION:  Close(var F);

      PURPOSE:  Closes a previously opened file.

         UNIT:  System

      REMARKS:  Where F is a file variable of any type that was
                previously opened with Reset, Rewrite, or Append.  The
                external file associated with F is updated and closed,
                and its DOS file handle is freed for reuse.

                NOTE: With {$I-}, errors are returned through IOResult