Continuations don't close over register stacks

[Luke Palmer]

Aren't continuations supposed to close over the register stacks?  In
this code:

    .sub _main
        I17 = 42
        savetop
        newsub P0, .Continuation, second
        restoretop
        invoke P0
    second:
        restoretop
        print I17
        print "\n"
        end
    .end

I should hope to get 42, but instead I get "no more I frames to pop."
They're not very good continuations if you have to treat them just like
an address stack!

Note that if they do, the code generated by the PCC constructs will have
to change to:

    savetop
    newsub P1, .RetContinuation, @retlabel
    invoke
    restoretop

Rather than saving right before the invoke.  This makes a lot more sense
to me, anyway.

Luke