death

[Henry Cejtin]

I won't deny the redundant aspect of passing around the sizes instead of
just re-evaluating Word8Array.length.  The whole original program was a
quick hack to see if I could do something for Rico that would be more space
efficient.
Is it always safe to call invariant()?  I would think that some times the
result would be an assertion failure even though all was legit because the
heap was partly changed or some live list was bogus.