bug report: picoseconds handling in System.Time

[Andrei Paskevich]

The diffClockTimes function can generate TimeDiff's with 
a negative value of tdPicosec. When you pass such a TimeDiff 
to addToClockTime, the latter may send negative picoseconds 
to toClockTime, provoking the error "picoseconds out of range".

While we are at it, please, teach normalizeTimeDiff to normalize
tdPicoSeconds, too. This misfeature hangs around for too long :)

Best regards,
Andrei

P.S. I'm not subscribed to the list, so please cc: me if needed.