REORG: config: move the http redirect rule parser to proto_http.c

We'll have to use this elsewhere soon, let's move it to the proper
place.
diff --git a/include/proto/proto_http.h b/include/proto/proto_http.h
index dd8367e..a379909 100644
--- a/include/proto/proto_http.h
+++ b/include/proto/proto_http.h
@@ -110,6 +110,8 @@
 struct http_req_rule *parse_http_req_cond(const char **args, const char *file, int linenum, struct proxy *proxy);
 void free_http_req_rules(struct list *r);
 struct chunk *http_error_message(struct session *s, int msgnum);
+struct redirect_rule *http_parse_redirect_rule(const char *file, int line, struct proxy *curproxy,
+                                               const char **args, char **errmsg);
 
 /* to be used when contents change in an HTTP message */
 #define http_msg_move_end(msg, bytes) do { \