minor improvements

Change-Id: Ia9872a613f3221e2de885f9d325a14f3c50b4beb

Signed-off-by: Christian Amend <chrisam@apache.org>
better server error messages in case of $format errors

Change-Id: If4495f5c91086618ee7d3824339aa5e7b99ff76c

Signed-off-by: Christian Amend <chrisam@apache.org>
better handling of parameters in server content negotiation

Change-Id: Ie2771940b3afea6efb3dc84f8322bc60069052d1

Signed-off-by: Christian Amend <chrisam@apache.org>