Fix more unicode kwargs dict keys (#302)

mopidy/models.py

@@ -127,11 +127,16 @@ def model_json_decoder(dct):
         {u'a_track': Track(artists=[], name=u'name')}
 
     """
+    # NOTE kwargs dict keys must be bytestrings to work on Python < 2.6.5
+    # See https://github.com/mopidy/mopidy/issues/302 for details.
     if '__model__' in dct:
         model_name = dct.pop('__model__')
         cls = globals().get(model_name, None)
         if issubclass(cls, ImmutableObject):
-            return cls(**dct)
+            kwargs = {}
+            for key, value in dct.items():
+                kwargs[str(key)] = value
+            return cls(**kwargs)
     return dct