Do not use the speculative compiler for functions with other than one
statement in the body, and do not use it if subexpressions can have
side effects.  Bailing out to the beginning of the full code is not
sound if side effects have already occurred.

Add tests that would fail without the restrictions.

Review URL: http://codereview.chromium.org/598016

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3826 ce2b1a6d-e550-0410-aec6-3dcde31c8c00