some testing hygene: move _reparse testing functionality to actual test support code, un-xfail a now passing test, reduce direct py.test.config usage aiming for deprecation.

--HG--
branch : trunk

testing/plugin/test_pytest_default.py

@@ -1,9 +1,9 @@
 import py
 from py.plugin.pytest_default import pytest_report_iteminfo
 
-def test_implied_different_sessions(tmpdir):
+def test_implied_different_sessions(testdir, tmpdir):
     def x(*args):
-        config = py.test.config._reparse([tmpdir] + list(args))
+        config = testdir.reparseconfig([tmpdir] + list(args))
         try:
             config.pluginmanager.do_configure(config)
         except ValueError: