setup: bump webtest minimum version to 2.0.6 to get py3 stdlib support /usr/lib64/python3.7/http/cookiejar.py:723: in is_third_party if not domain_match(req_host, reach(request.origin_req_host)): E AttributeError: '_RequestCookieAdapter' object has no attribute 'origin_req_host'

# requirements.txt file for use as "pip install -r requirements.txt" as a
# readthedocs compatible alternative to "pip install -e ." which is a working
# alternative to "setup.py develop" which doesn't work with Mercurial 3.7
.