SetTextBuf procedure

  DECLARATION:  SetTextBuf(var F : Text; var Buf [;Size : Word] );

      PURPOSE:  Assigns an I/O buffer to a text file

         UNIT:  System

      REMARKS:  F must be a Text file variable, Buf may be any variable, and
                Size is an optional Word type parameter.  Size may specify
                the size of the desired buffer in bytes.  If Size is omitted,
                SizeOf(Buf) is assumed; that is, the entire memory region
                occupied by Buf is used as a buffer.

                NOTE:  Calling SetTextBuf on an open file once I/O operations
                       have take place can cause data loss due to the change
                       of the buffer.

 RESTRICTIONS:  Must never be used on an open file, but may be called
                immediately after a call to Append, ReSet or ReWrite.

  DIFFERENCES:  Alternative to 3.0's syntax: Var F : Text[2048];