shims for running rails 3 with a rails 2 cache

 * serialized attributes format changed
 * associations are stored differently

Change-Id: I7a4739c333d295178f5fc11368a7b3e2f433da3b
Reviewed-on: https://gerrit.instructure.com/31671
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: James Williams  <jamesw@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>