While the flow graph is experimental, it's easier to be able to ignore
some problematic syntactic constructs.  Reduce the ones that can occur
in constructed flow graphs.

Review URL: http://codereview.chromium.org/790004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4084 ce2b1a6d-e550-0410-aec6-3dcde31c8c00