message: Add support for making attribute with TensorProto as value
  also fixes the bug of using plural "graph" field to store singular GraphProto value
diff: @@ -113,8 +113,10 @@ def make_attribute(key, value):
  # string
  elif bytes_or_false:
  attr.s = bytes_or_false
  + elif isinstance(value, TensorProto):
  + attr.t.CopyFrom(value)
  elif isinstance(value, GraphProto):
  - attr.graph.CopyFrom(value)
  + attr.g.CopyFrom(value)
  # third, iterable cases
  elif is_iterable:
  byte_array = [_to_bytes_or_false(v) for v in value]
  @@ -134,8 +136,7 @@ def make_attribute(key, value):
  "its applicable type.")
  else:
  raise ValueError(
  - "Your attribute {}:{} is not float, integer or string type, and is not"
  - "iterable.".format(key, str(value)))
  + 'Value "{}" is not valid attribute data type.'.format(value))
  return attr
  