MEDIUM: connection: add an error code in connections

This will be needed to improve error reporting, especially for SSL.
diff --git a/src/proto_http.c b/src/proto_http.c
index c01dfd2..0e51c08 100644
--- a/src/proto_http.c
+++ b/src/proto_http.c
@@ -4093,6 +4093,7 @@
 	s->req->cons->state     = s->req->cons->prev_state = SI_ST_INI;
 	s->req->cons->conn->t.sock.fd = -1; /* just to help with debugging */
 	s->req->cons->conn->flags = CO_FL_NONE;
+	s->req->cons->conn->err_code = CO_ER_NONE;
 	s->req->cons->err_type  = SI_ET_NONE;
 	s->req->cons->conn_retries = 0;  /* used for logging too */
 	s->req->cons->err_loc   = NULL;