Delegate to toStringRfc3339(). Previously toString() had three issues:
The last point also lost information because the time zone information was never printed leading to two dates with the same local time having the same string representation.
The implementation in toStringRfc3339() fixes these issues for all reasonable dates, but is not backwards compatible with the existing implementation. In particular it will include the time zone information and emit more digits to avoid rounding up.
Fix #590 (closed)