py3: use absolute_import in silenttestrunner.py

tests/silenttestrunner.py

@@ -1,4 +1,7 b''
-import unittest, sys, os
+from __future__ import absolute_import
+import unittest
+import sys
+import os
 
 def main(modulename):
     '''run the tests found in module, printing nothing when all tests pass'''

tests/test-check-py3-compat.t

@@ -49,7 +49,6 b''
   tests/readlink.py requires print_function
   tests/revlog-formatv0.py not using absolute_import
   tests/run-tests.py not using absolute_import
-  tests/silenttestrunner.py not using absolute_import
   tests/silenttestrunner.py requires print_function
   tests/sitecustomize.py not using absolute_import
   tests/svn-safe-append.py not using absolute_import