Whenever a user became active, this triggers an immediate presence
update event (to show that user as active). The implementation for
that event (running on the browsers of all other users in the realm)
would fully rerender the presence list, which can be an expensive
operation in a large realm, just to update the status for that one
user. This fixes that case to just remove the user from the list and
then re-insert it at the appropriate index.
[Commit message expanded with more details by Tim Abbott]
Vladislav Manchev