NodeBase metaclass check logic is faulty

[(removed)]

As hinted at on the ml, the NodeBase.new code is a bit faulty-

    def __new__(cls, name, bases, attrs):
        """
        Ensures that either a 'render' or 'render_iter' method is defined on
        any Node sub-class. This avoids potential infinite loops at runtime.
        """
        if not (isinstance(attrs.get('render'), types.FunctionType) or
                isinstance(attrs.get('iter_render'), types.FunctionType)):
            raise TypeError('Unable to create Node subclass without either "render" or "iter_render" method.')
        return type.__new__(cls, name, bases, attrs)

Failings:
1) for code that has already broken the iter_render/render cycle, each derivative *still* has to assign a render/iter_render else it'll invalidly explode
2) no way to disable it (intermediate direct descendants from Node, say, adding helper functionality- they expect render/iter_render to be overriden, but the rules don't apply to them).

Attached is a patch that converts the check over to verifying the resultant (as in, full MRO) render/iter_render, and adds an option to specifically disable the verification where needed.

[(removed)]

working version of the patch (using equality for the func check instead of identity)

[(removed)]

Fixed via [5511] removal, already fixed in 'upstream' (ie, my branch), thus closing since it won't be reappearing.