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

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

--- a/tests/test-annotate.t	Mon Jul 03 03:56:53 2017 +0200
+++ b/tests/test-annotate.t	Tue Aug 22 14:58:10 2017 -0400
@@ -400,7 +400,8 @@
 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,