updating rails to version 3.2.19
new model caching: rescue from undefined class or module error.

Trello:
https://trello.com/c/V6polddr/660-neues-konzept-fur-model-caching
new model caching: fixing marshal bug for inline caching.
making groups#show faster by caching the memberships using the new caching mechanism.

Trello:
https://trello.com/c/V6polddr/660-neues-konzept-fur-model-caching