As suggested by Tim Hunt.

Make sure things are throwing debugging notices and are documented.

MDL-40462 libraries: added another PHPUnit test to ensure deprecated function returns the same as the replacement

MDL-40431 libraries: added another PHPUnit test to ensure deprecated function returns the same as the replacement

Previously, even when a specific setting had to be returned, this method
would return an empty array. Now, the behaviour is the same whether
some options or none are set: if the requested setting is not found
null is returned.

MDL-40354 groups:groups_get_activity_allowed_groups() should use passed userid to check capabilities

Merge branch 'm26_MDL-39832_Fix_Chrome_Issues_ETag_XSendfile_2ndRound' of https://github.com/scara/moodle