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.

pkgs/top-level/python-packages.nix

@@ -21897,8 +21897,10 @@ in {
     };
   };
 
+  requests = self.requests2;
 
-  requests = buildPythonPackage rec {
+  # Remove before release of 17.09
+  requests_1 = buildPythonPackage rec {
     name = "requests-1.2.3";
     disabled = !pythonOlder "3.4";
 
@@ -21913,7 +21915,6 @@ in {
     };
   };
 
-
   requests2 = buildPythonPackage rec {
     name = "requests-${version}";
     version = "2.13.0";