add a way to mark hooks as "tryfirst" or "trylast" to influence its position in a hook chain.

Use 'tryfirst' for capturing hooks so they can start capturing as early as possible,
including when conftests add output in runtest_setup hooks.

_pytest/python.py

@@ -19,8 +19,8 @@ def pytest_cmdline_main(config):
         showfuncargs(config)
         return 0
 
-def pytest_namespace(__multicall__):
-    __multicall__.execute()
+@pytest.mark.trylast
+def pytest_namespace():
     raises.Exception = pytest.fail.Exception
     return {
         'raises' : raises,