Fix Python3 dup header handling.
Fixes isse #229.
diff --git a/Makefile b/Makefile
index 62931d8..fac0480 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,7 @@
 tests:
 	-cd python2 && python2.4 httplib2test.py
 	-cd python2 && python2.5 httplib2test.py
-	cd python2 && python2.6 httplib2test.py
+	-cd python2 && python2.6 httplib2test.py
 	cd python2 && python2.6 httplib2test_appengine.py
 	cd python2 && python2.7 httplib2test.py
 	cd python2 && python2.7 httplib2test_appengine.py