Refactored EditPage::getPreloadedText():

Refactored EditPage::getPreloadedText():
* Use WikiPage instead of Article (avoids conflicting with oldid url parameter)
* Use getRedirectTarget() instead of creating a new Title with the content of the page
* Changed userCanRead() calls to userCan( 'read' )
* Use "if ( something ) return;" instead of nesting if checks