Add pyutil as direct dependency; it was previously indirect dependency via zfec.

nix/tahoe-lafs.nix

@@ -4,7 +4,7 @@
 , setuptools, setuptoolsTrial, pyasn1, zope_interface
 , service-identity, pyyaml, magic-wormhole, treq, appdirs
 , beautifulsoup4, eliot, autobahn, cryptography
-, html5lib, future
+, html5lib, future, pyutil
 }:
 python.pkgs.buildPythonPackage rec {
   version = "1.14.0.dev";
@@ -50,7 +50,7 @@ python.pkgs.buildPythonPackage rec {
     setuptoolsTrial pyasn1 zope_interface
     service-identity pyyaml magic-wormhole treq
     eliot autobahn cryptography setuptools
-    future
+    future pyutil
   ];
 
   checkInputs = with python.pkgs; [

setup.py

@@ -124,6 +124,9 @@ install_requires = [
 
     # Support for Python 3 transition
     "future >= 0.18.2",
+
+    # Utility code:
+    "pyutil >= 3.3.0",
 ]
 
 setup_requires = [