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-45688 added missing library requirement
MDL-45686 qtype_multichoice get_num_selected_choices return wrong result
Merge branch 'MDL-45654-26' of https://github.com/rtcn2/moodle into MOODLE_26_STABLE
MDL-45499 admin: fixed error when displaying page settings
Merge branch 'MDL-42526-26' of git://github.com/jamiepratt/moodle into MOODLE_26_STABLE
Merge branch 'MDL-45607_m26' of https://github.com/markn86/moodle into MOODLE_26_STABLE
Merge branch 'm26_MDL-45623' of git://github.com/totara/moodle into MOODLE_26_STABLE
Merge branch 'MDL-45635-26' of git://github.com/andrewnicols/moodle into MOODLE_26_STABLE

Conflicts:
	lib/yui/src/notification/js/confirm.js
Merge branch 'MDL-45686_26' of git://github.com/jmvedrine/moodle into MOODLE_26_STABLE
Merge branch 'MDL-45660_26' of git://github.com/timhunt/moodle into MOODLE_26_STABLE
Merge branch 'MDL-45192_26' of git://github.com/dmonllao/moodle into MOODLE_26_STABLE
Merge branch 'MDL-45650_m26' of https://github.com/markn86/moodle into MOODLE_26_STABLE
MDL-45675 mod_data: initialise options as an empty array to avoid error when there are none
MDL-33763 notes: Fix issue with incorrect node highlighting in the nav tree
Merge branch 'MDL-44014-26' of git://github.com/andrewnicols/moodle into MOODLE_26_STABLE
Merge branch '45499-26' of git://github.com/samhemelryk/moodle into MOODLE_26_STABLE
MDL-45661 Assign: Clean bad data from DB after MDL-42526

Conflicts:
	mod/assign/db/upgrade.php
	mod/assign/version.php
Merge branch 'wip-MDL-45688-m26' of git://github.com/marinaglancy/moodle into MOODLE_26_STABLE