/* $DOC$
   $NAME$
      ft_Default()
   $CATEGORY$
      DOS/BIOS
   $ONELINER$
      Retrieve and optionally change the current default drive
   $SYNTAX$
      ft_Default( [ <cDrive> ] ) -> cDrive
   $ARGUMENTS$
      <cDrive> is optional, and if specified is the new default drive.
   $RETURNS$
      The current default drive.  If a change of default drive is requested,
      the return value is the drive AFTER the change is made.  This allows
      you to make sure you specified a valid drive (i.e. if you attempt to
      change the default drive, and the function returns a different drive
      letter than the one you specified, then the drive does not exist).
   $DESCRIPTION$
      Useful any time you need to know or change the default drive.
   $EXAMPLES$
      cDrive := ft_Default()  // Get the current drive
      ft_Default( "C" )       // Switch to drive C

      IF !( ft_Default( "E" ) == "E" )
         ? "Drive E does not exist!"
      ENDIF
   $END$
 */