This means we can now run things like running pylint --version without having
to set PYTHONPATH correctly now.
When using skip_install=true, the plugins wouldn't work as they need to import
qutebrowser.
We have to keep setting PYTHONPATH in run_pylint_on_tests.py, otherwise we get
this error I don't quite understand:
F: 1, 0: error while code parsing: Unable to load file
'/home/florian/proj/qutebrowser/git/__init__.py' ([Errno 2] No such
file or directory: '...') (parse-error)
If we do it in tox.ini, there are two drawbacks:
- We have more stuff in PYTHONPATH even if we don't when actually using
qutebrowser.
- The separator is platform specific, so we can't easily do this in a portable
way in tox.ini.
