[schema] restore constraint checking when running on old sqlite
Old sqlite3 doesn't provide CHECK constraint names in error messages,
preventing us from translating a backend integrity error into a
ValidationError. This was added in 2012, but the sqlite3 version in
RHEL6 is older; so if we run on old sqlite, keep checking the
constraints in python rather than only in SQL.
Closes #10927494
.. _req_module:
:mod:`cubicweb.req`
===================
.. automodule:: cubicweb.req
.. autoexception:: FindEntityError
.. autoclass:: RequestSessionBase
:members: