This is not covered by test262 yet, but it really makes sense and matches Firefox's behaviour.

TEST=mjsunit/define-properties.js
Review URL: http://codereview.chromium.org/8349031

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9694 ce2b1a6d-e550-0410-aec6-3dcde31c8c00