All the constructs that used it are now properly bracketed in the AST and we
handle abrupt exits without try/finally.  We can treat normal context exit
as occurring implicitly at the end of a body.

Review URL: http://codereview.chromium.org/7837025

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9189 ce2b1a6d-e550-0410-aec6-3dcde31c8c00