py3: use absolute_import in sitecustomize.py

tests/sitecustomize.py

@@ -1,3 +1,4 b''
+from __future__ import absolute_import
 import os
 
 if os.environ.get('COVERAGE_PROCESS_START'):

tests/test-check-py3-compat.t

@@ -45,7 +45,6 b''
   tests/readlink.py not using absolute_import
   tests/readlink.py requires print_function
   tests/run-tests.py not using absolute_import
-  tests/sitecustomize.py not using absolute_import
   tests/svn-safe-append.py not using absolute_import
   tests/svnxml.py not using absolute_import
   tests/test-atomictempfile.py not using absolute_import