unionrepo: dynamically create repository type from base repository...
unionrepo: dynamically create repository type from base repository
This is basically the same thing we just did for bundlerepo except
for union repositories.
.. api::
``unionrepo.unionrepository()`` is no longer usable on its own.
To instantiate an instance, call ``unionrepo.instance()`` or
``unionrepo.makeunionrepository()``.
Differential Revision:
https://phab.mercurial-scm.org/D4556