diffhelpers: use absolute_import

mercurial/pure/diffhelpers.py

@@ -5,6 +5,8
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
+from __future__ import absolute_import
+
 def addlines(fp, hunk, lena, lenb, a, b):
     while True:
         todoa = lena - len(a)

tests/test-check-py3-compat.t

@@ -122,7 +122,6
   mercurial/manifest.py not using absolute_import
   mercurial/mdiff.py not using absolute_import
   mercurial/patch.py not using absolute_import
-  mercurial/pure/diffhelpers.py not using absolute_import
   mercurial/pure/mpatch.py not using absolute_import
   mercurial/pure/osutil.py not using absolute_import
   mercurial/pure/parsers.py not using absolute_import