for review: allow `any' insts as non-local vars in higher-order terms

[Peter Schachte]

> 	In the long term we ought to look at adding support for
> 	some kind of `any -> the_same_any' mode which is like
> 	`any -> any' but which does not allow the argument to be
> 	bound.

FYI, HAL has this feature.  They use the name `unchanged,' and the idea is
that the value will not be any more constrained on exit than it was on call.
That does seem to be what is wanted here.  It's also easy enough to extend
it to cover free -> unchanged and bound(...) -> unchanged which are synonyms
for free -> free and bound(...) -> bound(...).  It's a bit weird, because
`unchanged' isn't an inst, but it does seem like a nice idea, if it's not
too much work. 


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