reftable: utility functions

This commit provides basic utility classes for the reftable library.

Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Helped-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/helper/test-reftable.c

@@ -0,0 +1,9 @@
+#include "reftable/reftable-tests.h"
+#include "test-tool.h"
+
+int cmd__reftable(int argc, const char **argv)
+{
+	basics_test_main(argc, argv);
+
+	return 0;
+}