fix pytest-xdist breakage

_pytest/__init__.py

@@ -1,2 +1,2 @@
 #
-__version__ = '2.1.0.dev6'
+__version__ = '2.1.0.dev7'

_pytest/assertion/__init__.py

@@ -68,7 +68,10 @@ def pytest_unconfigure(config):
     if hook is not None:
         sys.meta_path.remove(hook)
 
-def pytest_sessionstart(session):
+def pytest_collection(session):
+    # this hook is only called when test modules are collected
+    # so for example not in the master process of pytest-xdist
+    # (which does not collect test modules)
     hook = session.config._assertstate.hook
     if hook is not None:
         hook.set_session(session)

setup.py

@@ -22,7 +22,7 @@ def main():
         name='pytest',
         description='py.test: simple powerful testing with Python',
         long_description = long_description,
-        version='2.1.0.dev6',
+        version='2.1.0.dev7',
         url='http://pytest.org',
         license='MIT license',
         platforms=['unix', 'linux', 'osx', 'cygwin', 'win32'],