to avoid leaking of error objects to accessor methods when formatting
error messages internally.

Also, do not call overwritten toString methods on error objects when
formatting messages internally.

Review URL: http://codereview.chromium.org/6272004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6322 ce2b1a6d-e550-0410-aec6-3dcde31c8c00