pythonPackages.fs: build with all Python versions

and add updated explanation of why tests are disabled.
See also https://github.com/NixOS/nixpkgs/pull/13066

Changed files
+5 -4
pkgs
+5 -4
pkgs/top-level/python-packages.nix
···
${python.interpreter} -m unittest discover
'';
-
# Judging from SyntaxError
-
disabled = isPy3k;
-
-
# Lots of errors. Likely due to being in a chroot
+
# Because 2to3 is used the tests in $out need to be run.
+
# Both when using unittest and pytest this resulted in many errors,
+
# some Python byte/str errors, and others specific to resources tested.
+
# Failing tests due to the latter is to be expected with this type of package.
+
# Tests are therefore disabled.
doCheck = false;
meta = {