Merge pull request #1455 from benoit-pierre/fix_tests

tox: fix configuration so newer tox versions are supported

tox.ini

@@ -9,6 +9,12 @@ envlist=python
 
 [testenv]
 deps=-rtests/requirements.txt
+# Changed from default (`python -m pip ...`)
+# to prevent the current working directory
+# from being added to `sys.path`.
+install_command={envbindir}/pip install {opts} {packages}
+# Same as above.
+list_dependencies_command={envbindir}/pip freeze
 setenv=COVERAGE_FILE={toxworkdir}/.coverage.{envname}
 # TODO: The passed environment variables came from copying other tox.ini files
 # These should probably be individually annotated to explain what needs them.