rename exception attr to fields from items, add a test for it

colander/__init__.py

@@ -212,9 +212,9 @@ class UnsupportedFields(Invalid):
     cstruct during deserialize.
     """
 
-    def __init__(self, node, items, msg=None):
+    def __init__(self, node, fields, msg=None):
         super(UnsupportedFields, self).__init__(node, msg)
-        self.items = items
+        self.fields = fields
 
 
 class All(object):

colander/tests/test_colander.py

@@ -724,6 +724,7 @@ class TestMapping(unittest.TestCase):
         typ = self._makeOne(unknown='raise')
         e = invalid_exc(typ.deserialize, node, {'a':1, 'b':2})
         self.assertTrue(isinstance(e, colander.UnsupportedFields))
+        self.assertEqual(e.fields, {'b': 2})
         self.assertEqual(e.msg.interpolate(),
                          "Unrecognized keys in mapping: \"{'b': 2}\"")