[testlib] Use session.sessionid instead of deprecated session.id

Add data/pgdb to hgignore patterns PostgresTestDataBaseHandler uses it as datadir.

[test] make unittest_postgres pass Use PostgresApptestConfiguration which starts a postgresql cluster locally for the duration of the test.

[devtools] make PostgresTestDataBaseHandler start its own postgresql Don't depend on postgresql already running on the system, or on a static config. To use this, set the configcls attribute of your CubicWebTC-derived test class to PostgresApptestConfiguration. Caveats: - this won't work with several tests running concurrently from the same directory, since each would start its own cluster with a shared data directory and stomp on each other's toes - you need initdb/pg_ctl in $PATH, e.g /usr/lib/postgresql/$version/bin on Debian/Ubuntu systems. Closes #3489631

[web/staticcontrollers] create a unique temporary file for concat handling Predictable names means different processes can race against each other. Let's avoid that and use mkstemp to get a real unique temporary file, and atomically rename it when we're done. Closes #3524182

[server/repo] Use session.sessionid instead of session.id Silences deprecation warning.

[server/session] use _free_cnxset instead of free_cnxset to avoid warnings No need to make DeprecationWarning noise for something the user doesn't have any control over.

[server] Use internal_cnx instead of internal_session in init_repository