HTTP: improved getting of multi-valued headers in r.headersIn.
HTTP: improved getting of multi-valued headers in r.headersIn.

1) Duplicates of Content-Type, ETag, From, Max-Forwards, Referer,
   Proxy-Authorization, User-Agent are ignored.
2) Duplicate Cookie headers are joined together with ';'.
3) All other duplicate header values are joined together with ','.

nginx/njs,nginx/njs,nginx/njs,nginx/njs,nginx/njs,nginx/njs