Switching sides on the diff to correct Jenkins' display

This plugin sent me this link, which produced a diff that showed the opposite of reality.  This fixes the ordering of timestamps in the URL _and_ adds tests.

http://chocolate.factory.corp.yahoo.com:9999/jenkins/job/arya-build_container_distributor_test-subsystem_assembly/jobConfigHistory/showDiffFiles?timestamp1=2014-11-12_08-35-40&timestamp2=2014-11-12_08-35-39