ReSet procedure

  DECLARATION:  ReSet(var F [: File; RecSize : Word]);

      PURPOSE:  Opens an existing file

         UNIT:  System

      REMARKS:  F is a file variable of any type that must have been
                previously associated with an external file by the Assign
                procedure.  RecSize is an  optional word-type expression,
                which may only be specified if the file is untyped.

                If F was already open, it is first closed, then re-opened and
                the current pointer is moved to the beginning of the file.
                If F is a Text file, it becomes Read-Only.

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

  DIFFERENCES:  In 3.0, an empty filename was invalid.
                In 5.0, Assign(F,''), followed by ReSet(F), will refer to
                the standard input file (standard handle number 0).