MINOR: http: move redirect rule processing to its own function

We now have http_apply_redirect_rule() which does all the redirect-specific
job instead of having this inside http_process_req_common().

Also one of the benefit gained from uniformizing this code is that both
keep-alive and close response do emit the PR-- flags. The fix for the
flags could probably be backported to 1.4 though it's very minor.

The previous function http_perform_redirect() was becoming confusing
so it was renamed http_perform_server_redirect() since it only applies
to server-based redirection.
diff --git a/include/proto/proto_http.h b/include/proto/proto_http.h
index 48a606f..dd8367e 100644
--- a/include/proto/proto_http.h
+++ b/include/proto/proto_http.h
@@ -94,7 +94,7 @@
 		      char *sol, struct hdr_idx *idx,
 		      struct hdr_ctx *ctx);
 void http_sess_log(struct session *s);
-void perform_http_redirect(struct session *s, struct stream_interface *si);
+void http_perform_server_redirect(struct session *s, struct stream_interface *si);
 void http_return_srv_error(struct session *s, struct stream_interface *si);
 void http_capture_bad_message(struct error_snapshot *es, struct session *s,
                               struct http_msg *msg,