(#6962) Add integration tests on Face documentation.

We now run all the faces, and their actions, as well as global help through
the wringer in this test: this way we can be confident that we have, at least,
the ability to generate the help without a user-visible failure.

We also check that we have set copyright and license terms in our own faces.
Theoretically this might fail if the end user has extra faces on LOAD_PATH,
but my hope is that we won't hit that...