Fix issue #42 and issue #35
Fix issue #42 and issue #35

- #clear() now clears attributes as expected.
- #changedAttributes now behaves according to the test

afeld/backbone-nested,afeld/backbone-nested,GerHobbelt/backbone-nested,Mordentware/backbone-nested,Jaspersoft/backbone-nested,Mordentware/backbone-nested,wjb12/backbone-nested,Jaspersoft/backbone-nested,wjb12/backbone-nested