Fix bug introduced by commit 15298

git-svn-id: http://caml.inria.fr/svn/ocaml/version/4.02@15316 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
add a tests target to the Makefile

git-svn-id: http://caml.inria.fr/svn/ocaml/version/4.02@15317 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02