Deprecations for render_* methods

Do any deprecations need to go in to the render_* methods so they can
be reworked post 1.2? Not sure if there are plans for that, but looking
at the call tree for rendering an action produces quite a journey
through the rendering code.

Bob Silva

Those methods are there for performance and separation of concern
reasons. They're marked :nodoc:, though, and are protected. So if you
call them directly, you're relying on something that may well change in
the future. Consider them private and act accordingly.