DateTimeException if the given interval
is empty.
Example: -------------------- assert(NegInfInterval!Date(Date(2012, 3, 1)).contains( Interval!Date(Date(1990, 7, 6), Date(2000, 8, 2))));
assert(NegInfInterval!Date(Date(2012, 3, 1)).contains( Interval!Date(Date(1999, 1, 12), Date(2011, 9, 17))));
assert(!NegInfInterval!Date(Date(2012, 3, 1)).contains( Interval!Date(Date(1998, 2, 28), Date(2013, 5, 1)))); --------------------