[m-rev.] for review: allow pragmas to accept pred() and func() wrappers around symname/arity

[Zoltan Somogyi]

This implements what we discussed last week on m-dev.
For review by anyone. I would particularly like a quick
response to the change to prog_data.m, since any proposals
for better names for the notions described there would require
updating the rest of this diff.

I intend to add new test cases to invalid to test errors in the
newly allowed pragma forms, but will do this while this diff
is being reviewed.

I intend to document and announce the new functionality
only after we have used it ourselves without hitch for a
week or two.

After that, we can discuss whether to change how we treat
ambiguous pragmas, i.e. pragmas in which a symname/arity pair
can refer to either a predicate or a function. Currently, we
apply the pragma to both, which I think is unsafe, but we could
change it to generate an error in that case. I think Peter agrees,
since I am paraphrasing his suggestion, but maybe I am wrong.

Zoltan.
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