[test/tox] Enforce installation of modified yapps
580a6821713d is not enough for tox apparently...
The thing is that it will first install dependencies (the `deps` option from
tox.ini), actually pulling yapps from Logilab github but then, it will install
the project (that is, CubicWeb) from the sdist *along with its dependencies*,
which will pull yapps again and override the previously installed version for
some mysterious reason.
So add a `pip install` command in tox.ini, so that the modified yapps is the
last one installed.
Essayer le champ de recherche. Essayer des recherches comme "fiche
unmotachercher", ou encore "fiche wikiid index" ou "345".