REORG: http: move error codes production and processing to http.c

These error codes and messages are agnostic to the version, even if
they are represented as HTTP/1.0 messages. Ultimately they will have
to be transformed into internal HTTP messages to be used everywhere.

The HTTP/1.1 100 Continue message was turned to an IST and the local
copy in the Lua code was removed.
diff --git a/src/haproxy.c b/src/haproxy.c
index b993341..d596356 100644
--- a/src/haproxy.c
+++ b/src/haproxy.c
@@ -1447,6 +1447,11 @@
 	init_connection();
 	/* warning, we init buffers later */
 	init_pendconn();
+	if (!init_http(&err_msg)) {
+		ha_alert("%s. Aborting.\n", err_msg);
+		free(err_msg);
+		abort();
+	}
 	init_proto_http();
 
 	/* Initialise lua. */