Minor DaylightSaving bug

[Ellested]

When timeInYear is negative, and date is minValue, the date math is out of range.

[lahma]

As a side note, when I tested Jint against latest ECMA suite I found out that there's some trouble with really common dates like year -2000 that JS wants to comply with. So I think the underlying problem is a bit bigger, we shouldn't rely on .NET's DateTime being the internal representation of Date object, it cannot handle all the lovely features of JS.