Due to race conditions in the function subscribe_user
it was possible to create duplicate forum subscriptions.
This lead to error messages, when displaying the list of
all subscriptions.
This patch removes all existing duplicate entries and
creates a unique db key to prevent this from happening in
the future.
This change considers all existing search areas in Moodle and makes
necessary changes.
Custom change to course search, supported by helper in base.php:
* course/classes/search/mycourse.php
Custom change to message search:
* message/classes/search/message_received.php
* message/classes/search/message_sent.php
Custom change to user search:
* user/classes/search/user.php
Custom changes to module areas, supported by helper in base_mod.php:
* mod/book/classes/search/chapter.php
* mod/data/classes/search/entry.php
* mod/forum/classes/search/post.php
* mod/glossary/classes/search/entry.php
* mod/survey/classes/search/activity.php
* mod/wiki/classes/search/collaborative_page.php
(Note: the unit tests do not exhaustively check every context type
for these, given that's mainly handled by the helper function
which was already tested in the base_activity test.)
Handled by block base class (no change):
* blocks/html/classes/search/content.php
Handled by activity base class (no change):
* mod/assign/classes/search/activity.php
* mod/book/classes/search/activity.php
* mod/chat/classes/search/activity.php
* mod/choice/classes/search/activity.php
* mod/data/classes/search/activity.php
* mod/feedback/classes/search/activity.php
* mod/folder/classes/search/activity.php
* mod/forum/classes/search/activity.php
* mod/glossary/classes/search/activity.php
* mod/imscp/classes/search/activity.php
* mod/label/classes/search/activity.php
* mod/lesson/classes/search/activity.php
* mod/lti/classes/search/activity.php
* mod/page/classes/search/activity.php
* mod/quiz/classes/search/activity.php
* mod/resource/classes/search/activity.php
* mod/scorm/classes/search/activity.php
* mod/url/classes/search/activity.php
* mod/wiki/classes/search/activity.php
* mod/workshop/classes/search/activity.php
