Fixed all attr access: __getattr__, __setattr__, __delattr__.

The main work consisted of making sure that access is allowed and that
results are also proxied.
Change the test expectation that was failing for the C and Py proxy
version.
Implemented rich comparison operators as non-checked, which is what the C
implementation does.

Implemented __coerce__() in a special way, since _check_name did not work
for some reason.

All tests pass on Python 2.7.