The previous checkin (2.84) added a PyErr_Format call that made the
cost of raising an AttributeError much more expensive.  In general
this doesn't matter, except that checks for __init__ and
__del__ methods, where exceptions are caught and cleared in C, also
got much more expensive.

The fix is to split instance_getattr1 into two calls:

instance_getattr2 checks the instance and the class for the attribute
and returns it or returns NULL on error.  It does not raise an
exception.

instance_getattr1 does rexec checks, then calls instance_getattr2.  It
raises an exception if instance_getattr2 returns NULL.

PyInstance_New and instance_dealloc now call instance_getattr2
directly.