Refactoring and improvements of the accesslib.php library including prevention of access for not-logged-in users when forcelogin enabled, improved context caching, OOP refactoring of contexts, fixed context loading, deduplication of role definitions in user sessions, installation improvements, decoupling of enrolment checking from capability loading, added detection of deleted and non-existent users in has_capability(), new function accesslib test, auth and enrol upgrade notes.

More details are available in tracker subtasks.

MDL-28615 forum: Revised enrol_sharing_course to use the new enrol_get_shared_courses and fixed permission checking in forum_user_can_see_post

New PARAM_COMPONENT, PARAM_AREA and PARAM_PLUGIN + fixing of hopefully all current incorrect parameter types. This should help with diagnosing of incorrectly named 3rd party plugins too.

MDL-29189 mutlilang Reviewed the uses of course shortname and ensured things are being formatted consistently

MDL-23532 enrol - removed general handling of user enrolment editing/unenrolment plugins are now responsible for this

MDL-23532 enrol - moved UI enrolment components from core enrol to their respective enrolment plugins

As part of this patch I also introduced a new method in accesslib can_access_course that can be used
to check a users access to a course.
I also fixed a minor issue with guest access flag caching in require_login

 * fixed order of deleting in course adn context
 * adding course context to event data because it is not available alter and some stuff may depend on old context id
 * adding option for context purging (keeps the context record because it might be still referenced later and it would be recreated)
 * new course enrol cleanup
 * removing content from some course fields that were referencing deleted content
 * coding style and phpdocs improvements

MDL-21782 fixed wrong removal of hidden courses again - lot more thanks to Jay Knight for the report!

MDL-23237 new timecreated field in user_emrolments and adding timestart to enrol plugins that know it

MDL-23232 added support for enrol_plugin->all_enrol()  which indicates plugin allows users to add new enrolments manually

MDL-22780 sync ext db enrol when user logs in - except admins in case something goes really wrong in plugins