MDL-45654 cron: fix non-empty directories deletion

Remove errors when attempting to delete non-empty directories when
child directories do not get removed since the mtime was updated when
files were removed from the child directory.
MDL-42526 mod_assignment : fix record insert with assigment.id 0
MDL-45565 core_message: Fixed strangers array

Strangers get mixed with noreply user and support user,
if  noreply/support users real user.
To avoid duplication use userid as array index. Also,
avoid fetching data again for noreply and support users,
if they are real users, then data is already feteched.
MDL-45565 core_message: Added unit tests.
MDL-45686 qtype_multichoice get_num_selected_choices return wrong result
Merge branch 'MDL-45654-27' of https://github.com/rtcn2/moodle into MOODLE_27_STABLE
MDL-45499 admin: fixed error when displaying page settings
Merge branch 'MDL-42526-27' of git://github.com/jamiepratt/moodle into MOODLE_27_STABLE
MDL-45607 events: changed the context passed to the user_profile_viewed event
MDL-45623: Fix assigned users count on role delete confirmation page
MDL-45635 javascript: Make core dialogue translatable
Merge branch 'MDL-45686_27' of git://github.com/jmvedrine/moodle into MOODLE_27_STABLE
MDL-45660 question statistics: make comparison more robust.
MDL-45192 assign: added behat script & new definitions to handle alert dialog

The behat script is to test the batch action to lock and unlock submissions.
The new definitions are to prevent the "unexpected alert open" error in Selenium.
MDL-45192 behat: Replacing specific-selector steps by a generic one

Having a I click on we can use all our selectors rather
than having multiple steps for the same purpose. This
step allow us to manage JS native dialogues without
having to fail a scenario.

Credit for Mohamed Alsharaf.
MDL-45650 events: ensure correct objectid passed when triggering user_profile_viewed event
MDL-45675 mod_data: initialise options as an empty array to avoid error when there are none
MDL-45676 mod_data: added missing additional name fields
MDL-44014 Navigation: Set the correct context when retrieved via AJAX
MDL-45629 mod_assign: removed use of '$this->objectid' in the submission_status_viewed event