stack-discipline bug in 0.14 (recent)

Something somewhere seems to be forgetting to pop a frame off of the
temp stack.  Whatever that something somewhere is, it's apparently
not executed very often; one way of provoking it is to do:

? (describe *terminal-io*)

This'll crash in the middle of a MULTIPLE-VALUE-CALL; MV-CALL itself
doesn't seem to be the culprit, but it's certainly sensitive to seeing
something unexpected on the stack.

In that particular case, the "something unexpected" seems to be a
stack-consed list (perhaps a dynamic-extent &rest arg).

I suspect that this was recently introduced.