tests: update test-dirstate to pass our import checker

tests: update test-dirstate to pass our import checker

--- a/tests/test-dirstate.t	Tue Aug 22 15:50:35 2017 -0400
+++ b/tests/test-dirstate.t	Tue Aug 22 15:50:59 2017 -0400
@@ -66,7 +66,12 @@
 coherent (issue4353)
 
   $ cat > ../dirstateexception.py <<EOF
-  > from mercurial import merge, extensions, error
+  > from __future__ import absolute_import
+  > from mercurial import (
+  >   error,
+  >   extensions,
+  >   merge,
+  > )
   > 
   > def wraprecordupdates(orig, repo, actions, branchmerge):
   >     raise error.Abort("simulated error while recording dirstateupdates")