[merge] backport stable

[web/test] fix stale reference to the changelog view (closes #2423532)

Added tag cubicweb-debian-version-3.15.8-1 for changeset 4ef457479337

Added tag cubicweb-version-3.15.8 for changeset 459d0c48dfaf

[test] fix possible views test (closes #2544358)

prepare 3.15.8

[ldapfeed] if a deactivated user becomes available again in its source, reactivate it (closes #2542776) * cwusers that see their ldap source counterpart disappear are deactivated * until now they were not activated again on reappearance * note this behaviour in the doc

[ldaputils,ldapparser] correctly compute "deleted" users (closes #2542083) * in ldaputils.py, removal of an unneeded method (checking existence of an object in the ldap, but not using the configuration filters) * in the ldapparser, memoize the (filtered) search so as to serve both .process and .is_deleted * add a non regression test for the 'user-filter' source config entry + deletion

[dataimport] new ignore_errors argument to ucsvreader, default to False. Closes #2547200

[ldapsource] keep python 2.5 compatibility (closes #2541602)

[ldapuser2ldapfeed] .values -> .iteritems (closes #2542872)

[ldap tests] cleanup in preparation of #2542083

[ldapparser] demote warning level (actually important user info can leak there) (prepares #2542083)

Remove changelog view (closes #2423532)

[dataimport] Allow to replace escape char in the create_copyfrom_buffer

[doc] fix function name FTIRANK

[json] enable jsonexport selection on empty rsets (closes #2544358)

[test] fix req default value handling in CubicWebTC.view (closes #2544376) It's no more than the standard ``if rset`` vs. ``if rset is None`` error.

[ajax] fix attribute lookup (closes #2491038)

[server] add debugging for Hooks & Operations (closes #2470048)

[dataimport] Add SQL Store for faster import - works ONLY with Postgres for now, as it requires "copy from" command - closes #2410822 This store will use: - copy from for massive insertions. - execute from for update. The API of this store is similar to the other stores.

[test] swap order in assert of `test_users_and_groups_non_readable_by_guests` unittest2 order is (expected, got), not the opposite. This help test report readbility.

[test] fix server/querier/build_descr1 test. There is no self.transaction of TestCase. I assumed the test writer meant a session. This seems to make the test pass.

[server] make `test_bfss_fs_importing_transparency` less verbose on failure Dumping the whole content of a file on failure is a bit annoying. We only print the bad version here (it's usually the file path).