Add pytest 3 compatibility in brain_pytest

[The-Compiler]

This adds compatibility with pytest 3.0 to brain_pytest.py, where some attributes were added and others moved.

It also adds some failing attributes which are already present in older pytest versions, like pytest.xfail which existed for a long time.

In the second commit, I also re-added pytest 2.9 support (and it also seems to work fine with 2.7 still, didn't test older versions) as 3.0 is quite a big update and I don't expect everyone to upgrade immediately.

[The-Compiler]

I decided to do the assignments here instead of in an else: as there's no way this second line could raise an ImportError, and this makes the nested ImportErrors much more readable IMHO.

[The-Compiler]

Do I need to add myself to the copyrights, or will you run copyrite before the next release?

[coveralls]

Coverage decreased (-2.06%) to 86.961% when pulling cd757ca on The-Compiler:pytest3 into 3ea47e5 on PyCQA:master.

[coveralls]

Coverage remained the same at 89.016% when pulling 40913ed on The-Compiler:pytest3 into 3ea47e5 on PyCQA:master.

[coveralls]

Coverage remained the same at 89.016% when pulling 40913ed on The-Compiler:pytest3 into 3ea47e5 on PyCQA:master.

[PCManticore]

I can run it before the next release, you don't have to worried about that. Do you need a patch release or something? Since the default will go into 1.5.0, it could potentially take a while to be released, together with pylint 2.0, which is why I am asking.

[The-Compiler]

I think that would be great to have - I already have some suppressions for a no-member with pytest.xfail.

I'm not sure what happens after upgrading to pytest 3.0 - the old code snippet would probably raise an AttributeError, but I don't get any no-member messages anyways?