AthViews: Change SimpleView::proxy_exact to silently return failure.

ReadHandle is changing to prefer calling proxy_exact() to proxy(), as that's faster in most cases. If proxy_exact() fails, it falls back to proxy(). For now, change SimpleView::proxy_exact() to silently return failure so that ReadHandle will fall back to proxy(). It will be faster, though, if SimpleView can properly implement proxy_exact().

(cout deliberately left commented out for now).