bundlerepo: make bundle and bundlefile attributes private
These attributes are implementation details and shouldn't be
exposed outside the class.
.. api::
bundlerepo.bundlerepository.bundle and
bundlerepo.bundlerepository.bundlefile are now prefixed with an
underscore.
Differential Revision: https://phab.mercurial-scm.org/D1377
bundlerepo: don't assume there are only two bundle classes
exchange.readbundle() can return a type that represents a stream
clone bundle. Explicitly handle the bundle1 type and raise a
reasonable error message for unhandled bundle types.
Differential Revision: https://phab.mercurial-scm.org/D1376