A fixture with autouse set to False will always be used if it overrides a fixture with autouse set to True

• Include a detailed description of the bug or suggestion
  I took a look at pytest's source code and it looks like pytest records the names of all fixtures with autouse set to True. It then uses this list to determine which fixtures to use, even if the overriding fixture has autouse set to False.
• pytest and operating system versions
  platform linux2 -- Python 2.7.13, pytest-3.4.0, py-1.5.2, pluggy-0.6.0
• Minimal example if possible
  conftest.py

@pytest.fixture(autouse=True)
def foo():
    pass

test_me.py:

@pytest.fixture()
def foo():
    assert False

def test_bar(foo):
    pass

def test_baz():
    pass

Returns the following error:

____________________________________________________________________________ ERROR at setup of test_bar _____________________________________________________________________________

    @pytest.fixture()
    def foo():
>       assert False
E       assert False

____________________________________________________________________________ ERROR at setup of test_baz _____________________________________________________________________________

    @pytest.fixture()
    def foo():
>       assert False
E       assert False

I expect only test_bar to fail. Setting autouse to False for foo in conftest.py correctly causes only test_bar to fail.

Reproduce the fixture interaction using conftest.py and test_me.py with pytest's stated versions, then trace how autouse fixture names and overriding fixtures are selected. Confirm the fix by ensuring test_bar fails through its explicit fixture while test_baz does not use the overridden fixture.