error message in 'os.rename' does not include file name, because error

may be caused both by 'fromname' or 'toname'

loslib.c

@@ -1,5 +1,5 @@
 /*
-** $Id: loslib.c,v 1.38 2011/11/30 12:35:05 roberto Exp roberto $
+** $Id: loslib.c,v 1.39 2012/05/23 15:37:09 roberto Exp roberto $
 ** Standard Operating System library
 ** See Copyright Notice in lua.h
 */
@@ -98,7 +98,7 @@ static int os_remove (lua_State *L) {
 static int os_rename (lua_State *L) {
   const char *fromname = luaL_checkstring(L, 1);
   const char *toname = luaL_checkstring(L, 2);
-  return luaL_fileresult(L, rename(fromname, toname) == 0, fromname);
+  return luaL_fileresult(L, rename(fromname, toname) == 0, NULL);
 }