demandimport: use absolute_import

mercurial/demandimport.py

@@ -24,8 +24,11 b' These imports will not be delayed:'
   b = __import__(a)
 '''
 
-import os, sys
-from contextlib import contextmanager
+from __future__ import absolute_import
+
+import contextlib
+import os
+import sys
 
 # __builtin__ in Python 2, builtins in Python 3.
 try:
@@ -33,6 +36,8 b' try:'
 except ImportError:
     import builtins
 
+contextmanager = contextlib.contextmanager
+
 _origimport = __import__
 
 nothing = object()