Log Message:
Update to 2.7.1:

2.7.1 (compared to 2.7.0)
-----------------------------

- fix issue731: do not get confused by the braces which may be present
  and unbalanced in an object's repr while collapsing False
  explanations.  Thanks Carl Meyer for the report and test case.

- fix issue553: properly handling inspect.getsourcelines failures in
  FixtureLookupError which would lead to to an internal error,
  obfuscating the original problem. Thanks talljosh for initial
  diagnose/patch and Bruno Oliveira for final patch.

- fix issue660: properly report scope-mismatch-access errors
  independently from ordering of fixture arguments.  Also
  avoid the pytest internal traceback which does not provide
  information to the user. Thanks Holger Krekel.

- streamlined and documented release process.  Also all versions
  (in setup.py and documentation generation) are now read
  from _pytest/__init__.py. Thanks Holger Krekel.

- fixed docs to remove the notion that yield-fixtures are experimental.
  They are here to stay :)  Thanks Bruno Oliveira.

- Support building wheels by using environment markers for the
  requirements.  Thanks Ionel Maries Cristian.

- fixed regression to 2.6.4 which surfaced e.g. in lost stdout capture printing
  when tests raised SystemExit. Thanks Holger Krekel.

- reintroduced _pytest fixture of the pytester plugin which is used
  at least by pytest-xdist.