Fix possible double import of cubes modules When cubes using the new layout are imported with 'cubicweb_<cube>' and with 'cubes.<cube>', the same module is imported twice. Handle this by adding 'cubes.<cube>' to sys.modules when importing from 'cubicweb_<cube>'. Move load_module() to a sub class _CubesLoader to share informations computed in find_modules(). Don't handle subpackages in _CubesImporter and rely on normal import machinery instead. Add a test and use unittest from cubicweb.devtools.testlib which resolve to unittest2 on PY2 with assertLogs() method.

Make load_module() return existing module if present in sys.modules Otherwise the reload() builtin will not work correctly: https://www.python.org/dev/peps/pep-0302/#specification-part-1-the-importer-protocol

[server] Ignore computed relations in "relations" integrity checker

[server] Use global registry variable of integrity checker functions Instead of querying globals() in checkintegrity.check(), we maintain a _CHECKERS dict mapping checker name to function in checkintegrity module. This is later used to build the list of available checkers in 'db-check' command help.

[doc] Add 3.25 release notes [ci skip]

[repository] possibility to disable connections pooling Add a new configuration option 'connections-pooler-enabled' (default yes). If set to no, disable connection pooling and open new connections to the database on demand. This allow to use CubicWeb with other poolers (such as pgbouncer).