[m-rev.] diff: move contexts into goals in the parse tree

[Zoltan Somogyi]

This adds a couple of ZZZs, which I will fix soon.

It also starts a cleanup of library/term.m. I want to finish it, but
I think that should include moving the predicates related to type_to_term
to a new module. What do people think about that?

Zoltan.
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