Change-Id: Ib68ea809cbda50b445865bcde22ad7583c8e7f38
Allows overriding default behaviour for determining if a page exists.
If $isKnown is kept as null, regular checks happen. If it's a boolean, this value is returned by the isKnown method.
$title: Title object that is being checked
-$result: Boolean|null; whether MediaWiki currently thinks this page is known
+&$isKnown: Boolean|null; whether MediaWiki currently thinks this page is known
'TitleIsMovable': Called when determining if it is possible to move a page.
Note that this hook is not called for interwiki pages or pages in immovable namespaces: for these, isMovable() always returns false.