Use new subprocess32 when possible

pipeline/compilers/__init__.py

 from __future__ import unicode_literals
 
 import os
-import subprocess
+import sys
+
+if os.name == 'posix' and sys.version_info[0] < 3:
+    import subprocess32 as subprocess
+else:
+    import subprocess
+
 from tempfile import NamedTemporaryFile
 
 from django.contrib.staticfiles import finders

setup.py

 # -*- coding: utf-8 -*-
 import io
+import os
+import sys
 
 from setuptools import setup, find_packages
-import sys
 
 install_requires = []
 if (sys.version_info[0], sys.version_info[1]) < (3, 2):
     install_requires.append('futures>=2.1.3')
+if os.name == 'posix' and sys.version_info[0] < 3:
+    install_requires.append('subprocess32>=3.2.7')
 
 setup(
     name='django-pipeline',

tests/tests/test_compiler.py

@@ -7,7 +7,6 @@ from django.test import TestCase
 
 from pipeline.collector import default_collector
 from pipeline.compilers import Compiler, CompilerBase, SubProcessCompiler
-from pipeline.conf import settings
 from pipeline.exceptions import CompilerError
 
 from tests.utils import _, pipeline_settings

tox.ini

@@ -13,6 +13,7 @@ basepython =
 deps =
   py{27,py}: mock
   py{27,py}: futures
+  py{27,py}: subprocess32
   django18: Django>=1.8,<1.9
   django19: Django>=1.9,<1.10
   jinja2