fix bare "py.test" runs without a directory by not defaulting to --doctest-modules which will virtually import everything

bench/bench.py

@@ -1,4 +1,5 @@
 
+if __name__ == '__main__':
     import cProfile
     import py
     import pstats

tox.ini

@@ -63,6 +63,6 @@ commands=
 [pytest]
 minversion=2.0
 plugins=pytester
-addopts= -rxf --pyargs --doctest-modules
+addopts= -rxf --pyargs
 rsyncdirs=tox.ini pytest.py _pytest testing