Workaround for pytest-dev/pytest#1133

It seems that inside the tox environment `entry.path` points
to the local "pytestqt/logging.py" file (importable from $CWD).
Changing the current directory to "tests" during the tox run
worksaround this problem.

Author: nicoddemus

tox.ini

@@ -6,6 +6,7 @@ envlist = py{27,34}-pyqt4, py34-pyqt5, py{26,27,33,34}-pyside, docs
 [testenv]
 deps=pytest
     pyside: pyside
+changedir=tests
 commands=
     pyqt5: {envpython} scripts/link_pyqt.py --tox {envdir} 5
     pyqt4: {envpython} scripts/link_pyqt.py --tox {envdir} 4