Multiple WWW-Authenticate headers with "satisfy any;". If a module adds multiple WWW-Authenticate headers (ticket #485) to the response, linked in r->headers_out.www_authenticate, all headers are now cleared if another module later allows access. This change is a nop for standard modules, since the only access module which can add multiple WWW-Authenticate headers is the auth request module, and it is checked after other standard access modules. Though this might affect some third party access modules. Note that if a 3rd party module adds a single WWW-Authenticate header and not yet modified to set the header's next pointer to NULL, attempt to clear such a header with this change will result in a segmentation fault.