The xmlrpc is marked as deprecated [1]. Even if it's not now, the
legacy api is not marked as deprecated. So moving towards this one
sounds more reasonable [2].

[1] https://warehouse.readthedocs.io/api-reference/xml-rpc/#pypi-s-xml-rpc-methods

[2] https://warehouse.readthedocs.io/api-reference/legacy/#simple-project-api

Related T422

Based solely on pypi's deprecated xmlrpc api [1].  No other way of listing
pypi.org is referenced (except for parsing an html page through a
legacy api [2])

[1] https://warehouse.readthedocs.io/api-reference/xml-rpc/#pypi-s-xml-rpc-methods

[2] https://pypi.python.org/simple/

Related T422

That's needed for example for having the minimum necessary to make the
debian lister run.

This reverts commit e61512af.

This commit contains one section not supposed to be there yet (pypi is
not ready)

That's needed for example for having the minimum necessary to make the
debian lister run.

UnboundLocalError could happen otherwise

The api response json files used in tests were missing from the sdist
tarball created for package purposes, resulting in test failures.

Related T1137
Related T1138

Related T1138

Related T1138

Avoid eating *all* arbitrary arguments and passing them along to the
new_lister method.

Was missing the dict to read from

As response headers' keys are case-insensitive and requests does the
aggregation magic.

[1] http://docs.python-requests.org/en/master/user/quickstart/#response-headers