Monkey-patch httpretty for Python3 support

This fix is in the httpretty codebase, but not yet released

tests/unit/test_http_errors.py

@@ -1,6 +1,11 @@
 from __future__ import unicode_literals
 import json
 import httpretty
+
+# TEMP: Temporary hack until httpretty string checking is fixed
+if httpretty.compat.PY3:
+    httpretty.core.basestring = (bytes, str)
+
 try:
     import unittest2 as unittest # Python2.6
 except ImportError: