adapt to new refactored py baseline.

remove pickling in distributed testing
refactor internal mechanism enough to work for -n1
* * *
fix handling of crashing items and slave down events

testing/test_boxed.py

@@ -17,11 +17,9 @@ class TestOptionEffects:
     def test_boxed_option_default(self, testdir):
         tmpdir = testdir.tmpdir.ensure("subdir", dir=1)
         config = testdir.reparseconfig()
-        config.initsession()
         assert not config.option.boxed
         py.test.importorskip("execnet")
         config = testdir.reparseconfig(['-d', tmpdir])
-        config.initsession()
         assert not config.option.boxed
 
     def test_is_not_boxed_by_default(self, testdir):