Merge remote-tracking branch 'upstream/master' into mm

Conflicts:
	src/_pytest/main.py
	src/_pytest/mark/structures.py
	src/_pytest/python.py
	testing/test_main.py
	testing/test_parseopt.py

testing/test_helpconfig.py

@@ -3,6 +3,7 @@ from _pytest.config import ExitCode
 
 
 def test_version(testdir, pytestconfig):
+    testdir.monkeypatch.delenv("PYTEST_DISABLE_PLUGIN_AUTOLOAD")
     result = testdir.runpytest("--version")
     assert result.ret == 0
     # p = py.path.local(py.__file__).dirpath()