Message3299

As discussed on IRC I'm trying to change __findattr__ and __getattr__
roles, allowing *Derived classes to throw custom AttributeErrors without
a hack similar to what I did on #1038 (which does a double lookup when
it doesn't find anything).

I made the change on my hg repo
<https://hg.leosoto.com/jython.doj/rev/351f96f8e9cf>, and nothing seems
broken.

For consistency, I want to make a similar change for __finditem__ and
___getitem__ and then submit the patch here.

One thing I'm not sure about is the "__getattr__" name. As it is after
the change I made, it has the semantics of "__getattribute__". But then
we have "__setattr__", "__delattr__", etc, so I think it should keep the
"__getattr__" name, and a bit of documentation should avoid it be
misleading.