[m-rev.] for review: fix compiler abort after unresolved overloading

[Zoltan Somogyi]

This bug fix is relatively straighforward. The part most worth
looking at are the error message and the additions to list.m.
If anyone has better names for the new predicates there, speak up.
I will add a blurb the NEWS about them once we have settled
on a name.

Zoltan.
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