First version of static exceptions.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/static_exceptions@13217 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Use the typing environment to keep track of static handlers.  Hide static handlers under try blocks and lazy expressions.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/static_exceptions@13218 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02