changectx: use unfiltered changelog to walk ancestors in annotate

Since we are only walking ancestors, it is safe to use an unfiltered repository.
(Because if the original rev is not filtered, none of its ancestors will be).

Differential Revision: https://phab.mercurial-scm.org/D7501

mercurial/context.py

@@ -1161,7 +1161,9 b' class basefilectx(object):'
         # use linkrev to find the first changeset where self appeared
         base = self.introfilectx()
         if getattr(base, '_ancestrycontext', None) is None:
-            cl = self._repo.changelog
+            # it is safe to use an unfiltered repository here because we are
+            # walking ancestors only.
+            cl = self._repo.unfiltered().changelog
             if base.rev() is None:
                 # wctx is not inclusive, but works because _ancestrycontext
                 # is used to test filelog revisions

tests/test-repo-filters-tiptoe.t

@@ -136,13 +136,11 b' using annotate'
 - file with a single change
 
   $ hg annotate a
-  debug.filters: computing revision filter for "visible"
   0: a
 
 - file with multiple change
 
   $ hg annotate z
-  debug.filters: computing revision filter for "visible"
   0: some line
   1: in a
   2: file