peer: make ui an attribute With abc interfaces, instance attributes could not satisfy @abc.abstractproperty requirements because interface conformance was tested at type creation time. When we created the abc peer interfaces, we had to make "ui" a @property to satisfy abc. Now that peer interfaces are using zope.interface and there is no import time validation (but there are tests validating instances conform to the interface), we can go back to using regular object attributes. Differential Revision: https://phab.mercurial-scm.org/D3069