Actual Behavior

The (vendored_dirs .) stanza is not marking sub-directories as vendored.
I would expect this to work the same way as declaring the same directory as vendored from a parent directory:
(vendored_dirs sub) in root/dune vs
(vendored_dirs .) in root/sub/dune.

Reproduction

For example, using (vendored_dirs .) instead of (vendored_dirs *) in test/blackbox-tests/test-cases/vendor/duniverse/dune changes the test output.

Specifications

Using the dev version of Dune with OCaml 4.08.1.