tests: update test-annotate to pass our module import checker

tests/test-annotate.t

@@ -400,7 +400,8 b' and (2) the extension to allow filelog m'
 and its ancestor by overriding "repo._filecommit".
 
   $ cat > ../legacyrepo.py <<EOF
-  > from mercurial import node, error
+  > from __future__ import absolute_import
+  > from mercurial import error, node
   > def reposetup(ui, repo):
   >     class legacyrepo(repo.__class__):
   >         def _filecommit(self, fctx, manifest1, manifest2,