fix pytest protocol invocation to allow for module/session scoped fixtur...

This little change fixes pytest invocations to make fixtures more properly work.  Example of what is fixed:
```
import pytest

@pytest.fixture(scope="session")
def somefix():
      return object()

def test_1(somefix):
      assert 0, somefix

def test_2(somefix):
      assert 0, somefix
```

Without the fix the two failures will show two different ``somefix`` instances.   With the fix, they will be identical.

Note also that many others encountered this problem, see http://stackoverflow.com/questions/15875038/pydev-running-pytest-unit-test-with-module-shared-fixture-fails .