* (bug 20631) Preview of personal JavaScript and CSS pages now works again
* introduced SkinTemplate::$useHeadElement as switch for backward compatibility for extension skins using the old way of generating the <head> element:
** false (default): no change from previous version
** true: <head> specific items set in SkinTemplate::outputPage() are no longer generated (avoid double execution of some functions) and the result of OutputPage::headElement() is stored in the 'headelement' item
* updated all core skin to use this new method, some extensions using MonoBookTemplate but not extending SkinMonoBook (or for other core skins) will need to set $useHeadElement to true to work properly though
* Made Skin::userCanPreview() public since it's needed in OutputPage::getHeadScripts()
* Pass the Skin object from OutputPage::headElement() to OutputPage::getHeadScripts() rather than getting it from $wgUser