List of changes:
* New OOP API using PHP namespace \core\session\.
* All handlers now update the sessions table consistently.
* Experimental DB session support in Oracle.
* Full support for session file handler (filesystem locking required).
* New option for alternative session directory.
* Official memcached session handler support.
* Workaround for memcached version with non-functional gc.
* Improved security - forced session id regeneration.
* Improved compatibility with recent PHP releases.
* Fixed borked CSS during install in debug mode.
* Switched to file based sessions in new installs.
* DB session setting disappears if DB does not support sessions.
* DB session setting disappears if session handler specified in config.php.
* Fast purging of sessions used in request only.
* No legacy distinction - file, database and memcached support the same functionality.
* Session handler name included in performance info.
* Fixed user_loggedin and user_loggedout event triggering.
* Other minor bugfixing and improvements.
* Fixed database session segfault if MUC disposed before $DB.
Limitations:
* Session access time is now updated right after session start.
* Support for $CFG->sessionlockloggedinonly was removed.
* First request does not update userid in sessions table.
* The timeouts may break badly if server hosting forces PHP.ini session settings.
* The session GC is a lot slower, we do not rely on external session timeouts.
* There cannot be any hooks triggered at the session write time.
* File and memcached handlers do not support session lock acquire timeouts.
* Some low level PHP session functions can not be used directly in Moodle code.
GD PHP extension is now required. Add-ons need to remove $CFG->gdversion tests. The worst case regression is that add-on will think GD is not available.
Fixed 5 Moodle pages that does not display the course short name even if "Display extended course names" setting is on. In fixing this, search.php also included related minor code to change to minimise DB calls to improve performance.
All Days was set as the nothing value, but this nothing value was used.
Additionally, an insufficient comparison meant that the selecteddate then
became Today.
This commit coverts everything in the codebase to use the new
users_order_by_sql function when sorting lists of users. More details in
the bug.
Note that this does not change places where users are displayed in a
sortable table, and the sort order comes from the table.
