* The problem is that Title::userIsWatching() relies on $wgUser,
which is not suitable on every case. Instead User::isWatched()
requires both an User and a Title object.
* Replaced all core calls from the former to the latter
* Added a cache in User for the WatchedItem instances so we do not
need to do a database request every time something want to know
whether a page is watched or not, which can happen several times
per request.
Change-Id: Ifa9c55b7ffb487ce6893c74df233eedc7654dc5e
58852d8827