Constand should be case sensitive.

# Thanks Sterling

ext/standard/dir.c

@@ -141,7 +141,7 @@ PHP_MINIT_FUNCTION(dir)
 #endif
 	tmpstr[0] = DEFAULT_SLASH;
 	tmpstr[1] = '\0';
-	REGISTER_STRING_CONSTANT("DIRECTORY_SEPARATOR", tmpstr, CONST_PERSISTENT);
+	REGISTER_STRING_CONSTANT("DIRECTORY_SEPARATOR", tmpstr, CONST_CS|CONST_PERSISTENT);
 
 	return SUCCESS;
 }