pythonPackages.requests: point to requests2
pythonPackages.requests: point to requests2

The Python package has two packages for requests, `requests`
corresponding to version 1.2.3, and `requests2` corresponding to version
2.13.0. Version 1.2.3 is almost 4 years old, and by now all software
should have transitioned.

This commit aliases `requests` to `requests2`. Packages that stop to
function should be upgraded. In the rare case that that is not possible,
version 1.2.3 is still available as `requests_1` but I plan to drop
that before the release of 17.09.

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