modure: Upgrade re1.5 to 0.5.1

Changes include:

regexp.h: Add double-include protection.

extmod/re1.5/regexp.h

@@ -3,6 +3,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+#ifndef _RE1_5_REGEXP__H
+#define _RE1_5_REGEXP__H
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -136,3 +139,5 @@ int re1_5_sizecode(const char *re);
 int re1_5_compilecode(ByteProg *prog, const char *re);
 void re1_5_dumpcode(ByteProg *prog);
 void cleanmarks(ByteProg *prog);
+
+#endif /*_RE1_5_REGEXP__H*/