Fix getOwnPropertyDescriptor() support for index properties.

Fix getOwnPropertyDescriptor() support for index properties.

Add support for index properties with getters, setters or indexed interceptors.

For indexed interceptor case only fix crashes, do not guarantee any semantic soundness. Separate issue opened for this http://code.google.com/p/v8/issues/detail?id=877

BUG=http://code.google.com/p/v8/issues/detail?id=874

Review URL: http://codereview.chromium.org/3462005

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5512 ce2b1a6d-e550-0410-aec6-3dcde31c8c00