no className is passed and the invocant's class is Asset. This is
due to the root. In the db, the root Asset has the className WebGUI::Asset,
and the getRoot method matches this.
Changed the failing test in Asset.t to look for a WebGUI::Asset to be returned.
Added two tests to Asset.t to validate the object returned by Asset->getRoot method.
Reverted previous work and updated the POD for Asset->new.
000b2fcce3