Do not share internal data with other objects.

If we set a nested resource on an object, we do not want to take over
that object's internal data structures. We were accidentally using a
reference to the nested object's `data`. So when we we modified the
`data` of the parent object, the nested object would change as well.
Merge branch 'master' into josh/do_not_share_internal_data

Conflicts:
	spec/javascripts/associationsSpec.js
Merge pull request #89 from zendesk/josh/do_not_share_internal_data

Do not share internal data with other objects.