This behavior should not break any more use cases than before.
Previously, if the mismatch occured, we would actually push a manifest
that we then never referred to in the manifest list! If this was done in
a new repository, the command would fail with an obscure error from the
registry - the content wouldn't exist with the descriptor we expect it
to.
Signed-off-by: Justin Chadwell <me@jedevc.com>