revset: replace extpredicate by revsetpredicate of registrar This patch consists of changes below (these can't be applied separately). - replace revset.extpredicate by registrar.revsetpredicate in extensions - remove setup() on an instance named as revsetpredicate in uisetup()/extsetup() of each extensions registrar.revsetpredicate doesn't have setup() API. - put new entry for revsetpredicate into extraloaders in dispatch This causes implicit loading predicate functions at loading extension. This loading mechanism requires that an extension has an instance named as revsetpredicate, and this is reason why largefiles/__init__.py is also changed in this patch. Before this patch, test-revset.t tests that all decorated revset predicates are loaded by explicit setup() at once ("all or nothing"). Now, test-revset.t tests that any revset predicate isn't loaded at failure of loading extension, because loading itself is executed by dispatch and it can't be controlled on extension side.