auth: when a auth plugin can't be imported try the next one instead of breaking completly Some authentication modules depend on external services. This may cause the import to fail. Or another scenario is that a (third party) authentication module has been removed and can't be imported anymore.

# 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
.