Fix PR#6565: compilation fails with Env.Error(_)

git-svn-id: http://caml.inria.fr/svn/ocaml/version/4.02@15244 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Fix PR#6566: -short-paths and signature inclusion errors

git-svn-id: http://caml.inria.fr/svn/ocaml/version/4.02@15245 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
add test case for PR#6566

git-svn-id: http://caml.inria.fr/svn/ocaml/version/4.02@15246 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02