MINOR: actions: Regroup some info about HTTP rules in the same struct

Info used by HTTP rules manipulating the message itself are splitted in several
structures in the arg union. But it is possible to group all of them in a unique
struct. Now, <arg.http> is used by most of these rules, which contains:

  * <arg.http.i>   : an integer used as status code, nice/tos/mark/loglevel or
                     action id.
  * <arg.http.str> : an IST used as header name, reason string or auth realm.
  * <arg.http.fmt> : a log-format compatible expression
  * <arg.http.re>  : a regular expression used by replace rules
diff --git a/include/proto/http_ana.h b/include/proto/http_ana.h
index b324ea9..10ee78a 100644
--- a/include/proto/http_ana.h
+++ b/include/proto/http_ana.h
@@ -44,7 +44,7 @@
 			      struct ist name, const char *str, struct my_regex *re, int action);
 int http_req_replace_stline(int action, const char *replace, int len,
 			    struct proxy *px, struct stream *s);
-int http_res_set_status(unsigned int status, const char *reason, struct stream *s);
+int http_res_set_status(unsigned int status, struct ist reason, struct stream *s);
 void http_check_request_for_cacheability(struct stream *s, struct channel *req);
 void http_check_response_for_cacheability(struct stream *s, struct channel *res);
 void http_perform_server_redirect(struct stream *s, struct stream_interface *si);