Revert "removed test which is not valid anymore."

This reverts commit 9ede533f443e37772e645b15691bbc88d5070e36.
401 standard conformity
added reason to api.
test for the correct response.
rename X-ACCEPT-AUTH=X-Authentication-Scheme, test
test bugfix.
fixed tests.
intendation + changelog.
Merge pull request #209 from opf/feature/rails3_ajax_session_loss