This is the revision of break/continue patch I sent.
http://sparcs.kaist.ac.kr/~tinuviel/devel/ocaml/

This patch no longer modifies lambda code, and uses static exception
instead. bytegen is restored, and break/continue target stack is moved
to translcore.

simplify_exits is modified to track whether exit is in tail position.
It no longer replaces exit with handler when exit is not in tail
position. This is done with two hash tables; I'd like to hear
suggestions for better implementation.

-- 
Seo Sanghyeon