Automatic merge from submit-queue

WIP - Handle map[]struct{} in DeepCopy

Deep copy was not properly handling the empty struct case we use for Sets.

@lavalamp I need your expertise when you have some time - the go2idl parser is turning sets.String into the following tree:

    type:         sets.String           kind: Alias
      underlying: map[string]sets.Empty kind: Map
        key:      string                kind: Builtin
        elem:     set.Empty             kind: Struct
                                              ^
                                              should be Alias

Looking at tc.Named, I'm not sure what the expected outcome would be and why you flatten there.