* Add `popping-limits' components to block.

* Add `popping-limits' components to block.

* Change `ic-block?' to be non-integrable.

* Change `block-ancestry' to eliminate random extra argument.

* Define new procedure `block-partial-ancestry' which is like
`block-ancestry' except that it stops at a given ancestor.

* Make `stack-block/static-link?' be more sophisticated: static link
is not needed unless the block has some free variables.  Also, for IC
parent, check to see if lookup is being used on the parent.

* Define new procedures `block-original-parent', and
`{dis,}own-block-child!'.