Base attribute filtering on internal representation names

Instead on relying on the FriendlyName from metadatata, use the name
of the internal representation of an attribute in order to perform
filtering. Resolves #422

src/saml2/assertion.py

@@ -79,10 +79,15 @@ def filter_on_attributes(ava, required=None, optional=None, acs=None,
 
     def _match_attr_name(attr, ava):
         try:
-            friendly_name = attr["friendly_name"]
-        except KeyError:
-            friendly_name = get_local_name(acs, attr["name"],
+            friendly_name = get_local_name(acs, attr["name"], 
                                            attr["name_format"])
+        except:
+            friendly_name = None
+        if not friendly_name:
+            try:
+                friendly_name = attr["friendly_name"]
+            except KeyError:
+                pass
 
         _fn = _match(friendly_name, ava)
         if not _fn:  # In the unlikely case that someone has provided us with
@@ -91,6 +96,7 @@ def filter_on_attributes(ava, required=None, optional=None, acs=None,
 
         return _fn
 
+
     def _apply_attr_value_restrictions(attr, res, must=False):
         try:
             values = [av["text"] for av in attr["attribute_value"]]
@@ -105,7 +111,6 @@ def filter_on_attributes(ava, required=None, optional=None, acs=None,
         return _filter_values(ava[_fn], values, must)
 
     res = {}
-
     if required is None:
         required = []