BUG/MINOR: config: Copy default error messages when parsing of a backend starts

To be used, error messages declared in a default section must be copied when the
parsing of a proxy section starts. But this was only done for frontends.

This patch may be backported to older versions.
diff --git a/src/cfgparse.c b/src/cfgparse.c
index cef5e39..ab330a9 100644
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -2834,15 +2834,15 @@
 			curproxy->server_id_hdr_name = strdup(defproxy.server_id_hdr_name);
 		}
 
+		/* initialize error relocations */
+		for (rc = 0; rc < HTTP_ERR_SIZE; rc++)
+			chunk_dup(&curproxy->errmsg[rc], &defproxy.errmsg[rc]);
+
 		if (curproxy->cap & PR_CAP_FE) {
 			curproxy->maxconn = defproxy.maxconn;
 			curproxy->backlog = defproxy.backlog;
 			curproxy->fe_sps_lim = defproxy.fe_sps_lim;
 
-			/* initialize error relocations */
-			for (rc = 0; rc < HTTP_ERR_SIZE; rc++)
-				chunk_dup(&curproxy->errmsg[rc], &defproxy.errmsg[rc]);
-
 			curproxy->to_log = defproxy.to_log & ~LW_COOKIE & ~LW_REQHDR & ~ LW_RSPHDR;
 		}