Use pytest instead of py.test per upstream recommendation, #dropthedot

http://blog.pytest.org/2016/whats-new-in-pytest-30/
https://twitter.com/hashtag/dropthedot

example/boxed.txt

@@ -25,7 +25,7 @@ to run each test in a controlled subprocess.  Here is a basic example::
 
 If you run this with::
 
-    $ py.test -n1
+    $ pytest -n1
     =========================== test session starts ============================
     platform linux2 -- Python 2.7.3 -- pytest-2.3.0.dev8
     plugins: xdist, bugzilla, cache, oejskit, cli, pep8, cov
@@ -46,7 +46,7 @@ You'll see that a couple of tests are reported as crashing, indicated
 by lower-case ``f`` and the respective failure summary. You can also use
 the xdist-provided parallelization feature to speed up your testing::
 
-    $ py.test -n3
+    $ pytest -n3
     =========================== test session starts ============================
     platform linux2 -- Python 2.7.3 -- pytest-2.3.0.dev8
     plugins: xdist, bugzilla, cache, oejskit, cli, pep8, cov

example/loadscope/tox.ini

@@ -8,7 +8,7 @@ passenv = http_proxy https_proxy
 deps = -rrequirements.txt
 changedir = {envtmpdir}
 commands =
-    py.test -s -v \
+    pytest -s -v \
         --doctest-modules \
         --junitxml=tests.xml \
         --dist=loadscope \