Fix border radius on account navigation menu.
Review Request #3489 - Created Nov. 10, 2012 and submitted
This fixes a minor styling issue where all items in the account navigation have rounded borders (on the bottom left and bottom right) in the hover state, when only the last item needs this styling applied.
Verified on Chrome, Safari, Firefox (all latest). Did not test in IE (no access to Windows at the moment). :last-child isn't supported for IE < 9, but neither is border-radius, so it shouldn't affect older versions of IE.