message: _DefinedFunction.name should be a string.
  With the C API enabled and python2, it was being set to a unicode
  object.
diff: @@ -417,7 +417,7 @@ class _DefinedFunction(object):
  if self._func_name:
  assert self._func_name == self._op_def.name
  else:
  - self._func_name = self._op_def.name
  + self._func_name = compat.as_str(self._op_def.name)
  def _set_c_attrs(self, attrs):
  """Sets `attrs` as attributes of self._c_func.
  