[server] drop system_source_cnx for a simpler internal API system_source_cnx() can be replaced with source_cnx(). If system_source_cnx() is called with dbms_system_base=False, it is strictly equivalent to calling source_cnx() with the same source, privileges and interactivity. If system_source_cnx() is called with dbms_system_base=True, it is equivalent to calling source_cnx() with the system database and the same source, privileges and interactivity. No use of the default value for 'special_privs' was found in the code.

3.26 (1 February 2018)
======================

New features
------------

* For ``pyramid`` instance configuration kind, logging is not handled anymore
  by CubicWeb but should be configured through ``development.ini`` file
  following https://docs.pylonsproject.org/projects/pyramid/en/latest/narr/logging.html.

Backwards incompatible changes
------------------------------

* CubicWebConfiguration method 'shared_dir' got dropped.