pytest migration: simplify hg+git test class hierarchies No need to use multiple inheritance when single inheritance can do it just as well. Let the git/hg test cases just derive from _BaseTestCase which in turn derives from TestControllerPytest. Also remove empty setup_class/teardown_class methods.

# 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
.