maps.flan and map-exhausted.flan as fixed-output cases, the six refusals
by name, and map-stale-region.flan beside stale-region.flan.
The last one is not a line in the Vec's program because the two reach
the check by different routes. A Vec's operations check on the way in
and stop there. A map's get goes on to call a hash and an equality
function through pointers into the block, so a missing check there is
not a wrong number — it is a probe loop walking released memory. It
traps naming the site and exits 134, as the Vec's does.
{K V} resolves now, so the test that asserted it was milestone 6 is
replaced by the one that still holds: the arity, refused for the reason
Vec's arity is refused, because a near-miss would otherwise resolve to a
type variable and come back as generics.