rework acs::test::http interface to allow daisy chaining of requests. One can now specify "-last_reqest" to let a new http to continue with the same credentials (e.g. cookies) as the last request. The old interface based on "-user_id" continues to work
acs::test::form_reply: add option "-remove" in analogy to "-update" to remove entries from the provided dict. This is necessary for web regression testing for check boxes, where the application has to decuce from the fact, that a field is not transmitted, that a value has to be changed.