Adds $wgEchoSectionTransition and $wgEchoBundleTransition.
If either of these settings is enabled, we will disbelieve
the alert/message counts in the euw table and obtain them
using server-side cross-wiki API queries instead.
This affects both ApiEchoNotifications (for generating the cross-wiki
summary entry) and the count and timestamp computation in NotifUser.
In bundle transition mode, we trust that notifications are classified
correctly between alerts and messages, but we don't trust the
counts in the table. In section transition mode, we trust that
the sum of the alert and message counts is the correct count,
but we don't trust the alert and message counts individually.
If both modes are enabled, we mistrust anything that's mistrusted
by either mode and only trust what's trusted by both modes.
In any event, we do trust that only the wikis with rows in the
euw table have unread notifications.
Bug: T132954
Change-Id: Ibcc8ac102dac3cf06916d67427b42457fdb93db6
The query shouldn't be too expensive: it'll use an index to narrow
down the resultset for 1 user. After that, it'll be sorted based on
a grouped by value, but that should fit in memory: it'll never be
on more than 2000 entries, which is the max amount of notifications
per user.
Change-Id: I271ea7f7a6e010284739bfce02c4ec8a077148fc
