split boolify_iter into two ops, for hash and array.
waste one less bit in facts bitfield
boolify_iter_hash and _arr in the jit, too.
Neither iterating over a hash or an array is certain

In other words, I was wrong about the two being mutually
exclusive, since neither of them may actually be set.
This still fails a few spectests, though.
jit gcd_I, too. should make much more rat computation work
Merge branch 'split_iter_boolification'

With this, we get three ops for boolifying iterators:
one for array iterators, one for hash iterators and one in case we don't
know for sure.