[PATCH] Compliance: respond to OPTIONS requests with zero Max-Forwards value.

Compliance: respond to OPTIONS requests with zero Max-Forwards value.

RFC 2616 section 9.2 says that a proxy MUST NOT forward requests with
a zero Max-Forwards value. RFC 2616 does not define proper OPTIONS
responses, so we consider successful responses optional and reply with
501 Not Implemented.

While TRACE and OPTIONS are similar with regard to Max-Forwards, we
handle them in different places because OPTIONS do not need to echo the
request via Store.

Co-Advisor test case: test_case/rfc2616/maxForwardsZero-OPTIONS-absolute