This fixes installation of swh modules in virtualenv when executing $ pip install $(./bin/pip-swh-packages) in swh-environment.

The following error is reported otherwise and all modules get uninstalled afterwards.

ERROR: swh-storage 0.0.178 has requirement swh.core[db,http]==0.0.94, but you'll have swh-core 0.0.94.post1 which is incompatible.