- hs-pick-first/last/random/items/slice: short-circuit nil or non-list
(strings flow through unchanged).
- New hs-pick-match / hs-pick-matches wrappers around regex-match /
regex-find-all, also nil-safe; compiler routes pick-match / pick-matches
through them. Unblocks 'pick first from null returns null' and
'pick match from null returns null' which previously looped past
step_limit.
giles
5b31d935bd