Stream is not Serializable, which is confusing for users and causes lub-computation to infer a type of 250 lines

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Stream shares the fate of List: Stream.Empty and Stream.Cons are Serializable, but Stream itself is not.

Related to #7402.

A potential issue is that unlike List, Stream is not sealed.

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Imported From: https://issues.scala-lang.org/browse/SI-7403?orig=1
Reporter: @soc
Affected Versions: 2.10.1, 2.11.0-M2
See #7402

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@adriaanm said:
shall we deprecate Stream's un-sealedness?

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@soc said:
That's what I would have proposed. Add "@deprecatedInheritance" and "with Serialization".

I can do it.

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@soc said:
Merged in scala/scala@d6b205c.

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@lrytz said:
test in scala/scala#4409