require 'six' in setup.py, add flask._compat for stuff not yet in 'six'

flask/_compat.py

@@ -0,0 +1,13 @@
+# -*- coding: utf-8 -*-
+"""
+    flask._compat
+    ~~~~~~~~~~~~~
+
+    Some py2/py3 compatibility support that is not yet available in
+    "six" 1.3.0.
+    There are bugs open for "six" for all this stuff, so we can remove it
+    again from here as soon as we require a new enough "six" release.
+
+    :copyright: (c) 2013 by Armin Ronacher.
+    :license: BSD, see LICENSE for more details.
+"""

setup.py

@@ -90,6 +90,7 @@ setup(
     zip_safe=False,
     platforms='any',
     install_requires=[
+        'six>=1.3.0',
         'Werkzeug>=0.7',
         'Jinja2>=2.4',
         'itsdangerous>=0.17'