fix cache forcing for rails 3

just use stubs, so we don't hide switchman's extensions

Change-Id: I65012c7221ce02f355035746ed06d42220af59b7
Reviewed-on: https://gerrit.instructure.com/31716
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>