SquidUpdate, Title, DynamicPageList
This code aims to fix bug 20818 squid caching issues.
First, SquidUpdate::newFromTitles() is changed to be based on getSquidURLs() instead of generating the url by itself. This probably fixes caching problems on wikis with variants.
Second, TitleSquidURLs hook is added to allow extensions to add extra article-related urls which need purging.
Third, DynamicPageList is modified to use the new hook to purge the ?curid urls it generates.
attachment bug 21032.patch ignored as obsolete