plus more accurate distinction of different change types.

Required handlifying more code.

Also fixed a handlification bug in JSProxy::GetElementAttributeWithHandler.

R=verwaest@chromium.org
BUG=

Review URL: https://codereview.chromium.org/11362115

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12888 ce2b1a6d-e550-0410-aec6-3dcde31c8c00