py3: use absolute_import in test-revlog-ancestry.py

tests/test-check-py3-compat.t

@@ -62,7 +62,6 b''
   tests/test-manifest.py not using absolute_import
   tests/test-pathencode.py not using absolute_import
   tests/test-pathencode.py requires print_function
-  tests/test-revlog-ancestry.py not using absolute_import
   tests/test-revlog-ancestry.py requires print_function
   tests/test-run-tests.py not using absolute_import
   tests/test-simplemerge.py not using absolute_import

tests/test-revlog-ancestry.py

@@ -1,5 +1,10 b''
+from __future__ import absolute_import
 import os
-from mercurial import hg, ui, merge
+from mercurial import (
+    hg,
+    merge,
+    ui,
+)
 
 u = ui.ui()