py3: change default priority and length used for sorting hooks to be compatible with python 3 The call to `sorted(hooks.values())` can on line 213 of hooks.py can raise when using python 3. For instance, when hooks.values is `[(0, 2, b'post-commit.check-status', b''), (None, None, b'changegroup.app-hooks', <object object at 0x7f5279885590>)]`, the error is `TypeError: '<' not supported between instances of 'NoneType' and 'int'` This fix keeps the same order that was used in python 2 without relying on comparison with None. Differential Revision: https://phab.mercurial-scm.org/D8527