Tune Skin::preloadExistence

Just preload user page and talk, when the personal bar is shown.
Use Skin::getRelevantTitle for the title to have the correct title
preloaded, when using for example [[Special:WhatLinksHere]].

Change-Id: I4363a9f3fd909cfdc341dc1a8c6c0189efd9b736
Merge "Tune Skin::preloadExistence"