* Modified Article::loadPageData() to use a slave database connection and pageDataFro...

* Modified Article::loadPageData() to use a slave database connection and pageDataFromTitle() instead of pageDataFromId() in the default case, as in Wiki.php (this also saves a query since the ID will be fetched with other fileds)
* Removed the loadPageData() call for the initial article in Wiki.php, will be triggered by the isRedirect() call 7 lines below if needed (this was not needed if $target is set by the InitializeArticleMaybeRedirect hook), but kept the second one (same as above, Article::exists() triggers Title::getArticleId() that would use one query to get id and a second one is needed to get the complete page data)
* Modified Article::fetchContent() to use common code (loadPageData()) and to only call it if really needed