What does this bit of code do?

[Kent M Pitman <KMP@STONY-BROOK.SCRC.Symbolics.COM>]

I happen to agree with you, but it is a point more controversy than I
would have expected. We had a lot of discussion about it internally at
Symbolics a while back. In any case, nailing down the semantics of
non-local exit from UNWIND-PROTECT is on my list of changes to submit 
to the cleanup committee in the very near future. (To those not on
that committee, don't panic -- we don't actually make any decisions,
we just package up the space of options into ballot items that can be
voted upon by X3J13.)