Add test to verify #25
Fix looking up the proper serialized value in an Exposed obj hierarchy

This improves the serialized value look-up process by checking own properties first, before walking the prototype chain to find parent values.

Fixes #25
Remove unused var
Add HISTORY entry for #25
Remove TODO comment that's no longer valid

This "concern" no longer applies because we're always checking own properties for their values, and when we walk the prototype, we make sure it's an exposed instance.
Merge pull request #26 from yahoo/override-serialized-value

Fix looking up the proper serialized value in an Exposed obj hierarchy