[ IMPROVEMENTS ]
DateTime::Duration now provides a compare() class method.
DateTime::Duration now overloads comparison to throw an exception,
because comparison requires a base DateTime object. Note that
previous versions of DateTime::Duration did not overload
comparison, so if you were comparing them, you were just comparing
the value of the object references. Thanks to Rick Measham, Jon
Swartz, and Max Maischein for contributing to the discussion on
datetime@perl.org about how to implement this feature.