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	Fixup to hoistForAllTys
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* hoistForAllTys moves from TcHsType to TcType

hoistForAllTys was being too vigorous and breaking up type synonyms,
even when it was entirely unnecessary to do so.

Not only does this make error messsages less good, but it's actually
wrong for Haskell 98, because we are meant to report under-applied
type synonyms, and that check doesn't happen until after hoistForAllTys.
This led to a very obscure bug, immortalised as tcfail129.