inhibit: add test to ensure that --hidden is working with inhibit
There was a concern with the transaction hook in inhibit and its potentially
devastating effect when used with --hidden. The transaction hook in inhibit
hides all the visible & obsolete commits when the transaction ends using the
visible() and the obsolete() revset.
--hidden does not change the visible() revset so it is fine. If this changes in
the future and --hidden actually ends up impacting the visible() revset, this
test will catch it and prevent inhibit from putting inhibition markers on
all of the obsolete changesets.