In addition, this fixes defineOwnProperty to actually not throw when
the should_throw flag is false (we had no usage of this priorly).

Review URL: http://codereview.chromium.org/6695018

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7176 ce2b1a6d-e550-0410-aec6-3dcde31c8c00