python.pkgs.virtualenv: move to separate expression

pkgs/development/python-modules/virtualenv/default.nix

@@ -0,0 +1,31 @@
+{ buildPythonPackage
+, fetchPypi
+, lib
+, recursivePthLoader
+}:
+
+buildPythonPackage rec {
+  pname = "virtualenv";
+  version = "15.0.3";
+  name = "${pname}-${version}";
+
+  src = fetchPypi {
+    inherit pname version;
+    sha256 = "6d9c760d3fc5fa0894b0f99b9de82a4647e1164f0b700a7f99055034bf548b1d";
+  };
+
+  # Doubt this is needed - FRidh 2017-07-07
+  pythonPath = [ recursivePthLoader ];
+
+  patches = [ ./virtualenv-change-prefix.patch ];
+
+  # Tarball doesn't contain tests
+  doCheck = false;
+
+  meta = {
+    description = "A tool to create isolated Python environments";
+    homepage = http://www.virtualenv.org;
+    license = lib.licenses.mit;
+    maintainers = with lib.maintainers; [ goibhniu ];
+  };
+}