DSTon
| tDAYZONE { param->yyTimezone = $1; param->yyDSTmode = DSTon; }
| tZONE tDST { param->yyTimezone = $1; param->yyDSTmode = DSTon; }
case DSTon: tm.tm_isdst = 1; break;
if (DSTmode == DSTon) /* if specified sumer time */