Fix pickle.loads crashing on non-ASCII chars.

Thanks to Shay Erlichmen.
diff --git a/flask_openid.py b/flask_openid.py
index fe8496b..a02f521 100644
--- a/flask_openid.py
+++ b/flask_openid.py
@@ -114,7 +114,7 @@
     def __getitem__(self, name):
         rv = session[self.name_mapping.get(name, name)]
         if isinstance(rv, dict) and len(rv) == 1 and ' p' in rv:
-            return pickle.loads(rv[' p'])
+            return pickle.loads(rv[' p'].encode('utf-8'))
         return rv
 
     def __setitem__(self, name, value):