fix bad handling of inlined relations when entities of different etypes are passed as subject to add_relations

fix failing test_migration test caused by schema change

fix tests broken by fcb8932082a5

merge back stable

fix server/test/unittest_checkintegrity (failing since 70538ea2532d)

fix implementation of repository.glob_add_relations (closes ##1625257) the internal data structure had changed during implementation and the code had not been updated...

[server] improve the speed of setting relations between entities (closes #1625257) The main idea is to add methods equivalent to session.add_relation and repository.glob_add_relation which handle several relations in one call. Speed gain results from: * using cursor.executemany to run SQL statements * factorizing some code which otherwise has to be performed for each relation, such as context manager creation before calling hooks or to enable security, creation of the EditedEntity instance (when several inlined relations are set on a single entity, and consequently when refreshing the cached entity) benchmark runs 1.1x faster for non inlined entities and 125x faster for inlined entities :-)

added test case to monitor speed improvements in the repository code. To use it, add a test in a patch, then hack CW to speed it up in another patch, updating the test if needed. By running the test with and without the second patch applied you can easily see the speed improvements