fixed removal of built extensions in tox.ini

tox.ini

@@ -11,11 +11,13 @@ envlist = py26, py27, py32, py33
 deps =
     -r{toxinidir}/requirements.txt
     -r{toxinidir}/test_requirements.txt
+whitelist_externals =
+    make
 commands =
     # run tests both with and without the C extensions (including Cython)
     {envpython} setup.py --quiet build_ext --inplace
     {envbindir}/nose2 --no-user-config tests
-    {envpython} setup.py --quiet build_ext --inplace
+    make clean-build-ext-inplace
     {envbindir}/nose2 --no-user-config tests
 
 [testenv:py26]