[schema] drop monkeypatch "name_for" on BaseConstraint
BaseConstraint doesn't have "name_for" method, this is just an addition for
cubicweb needs.
Implement this as a function instead of a monkeypatch to avoid having
"name_for" not defined because cubicweb.schema hasn't been imported.
In particular this fix running cubicweb/server/test/unittest_schema2sql.py::SQLSchemaTC::test_known_values alone.
missing-dep-for-interpreter make => make | build-essential | dpkg-dev (usr/*/cubicweb/skeleton/debian/rules)
embedded-javascript-library usr/share/cubicweb/cubes/shared/data/jquery.js