(fixes bug 619).

This also fixes a bug in GetOwnProperty in runtime.cc discovered by
the new test cases. That part of the code was not testable before
since we had no way of correctly defining properties on elements.

Review URL: http://codereview.chromium.org/2832001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4862 ce2b1a6d-e550-0410-aec6-3dcde31c8c00