REORG: http: move some header value processing functions to http.c

REORG: http: move some header value processing functions to http.c

The following functions only deal with header field values and are agnostic
to the HTTP version so they were moved to http.c :

http_header_match2(), find_hdr_value_end(), find_cookie_value_end(),
extract_cookie_value(), parse_qvalue(), http_find_url_param_pos(),
http_find_next_url_param().

Those lacking the "http_" prefix were modified to have it.