Fix opmitized external array access for compound assignments and count operations, also implement missing ARM typed array Hydrogen loads and stores.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/6805005

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7536 ce2b1a6d-e550-0410-aec6-3dcde31c8c00