don't load associations when marshalling records in rails 3

Change-Id: I97b89d79fed24b8ac7de7da3f37e519017889ce6
Reviewed-on: https://gerrit.instructure.com/30997
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>