SSI: fixed $date_local and $date_gmt without SSI (ticket #230). If there is no SSI context in a given request at a given time, the $date_local and $date_gmt variables used "%s" format, instead of "%A, %d-%b-%Y %H:%M:%S %Z" documented as the default and used if there is SSI module context and timefmt wasn't modified using the "config" SSI command. While use of these variables outside of the SSI evaluation isn't strictly valid, previous behaviour is certainly inconsistent, hence the fix.