Added parameter to BeforePageDisplay hook so that extension can use it to modify it. See my next commit for an inplementation of it.

docs/hooks.txt

@@ -429,7 +429,8 @@ rendered inline in wiki pages or galleries in category pages.
 &$time: image timestamp
 
 'BeforePageDisplay': Prior to outputting a page
-$out: OutputPage object
+&$out: OutputPage object
+&$skin: Skin object
 
 'BeforeParserFetchTemplateAndtitle': before a template is fetched by Parser
 &$parser: Parser object

includes/OutputPage.php

@@ -781,7 +781,7 @@ class OutputPage {
 		} else {
 			// Hook that allows last minute changes to the output page, e.g.
 			// adding of CSS or Javascript by extensions.
-			wfRunHooks( 'BeforePageDisplay', array( &$this ) );
+			wfRunHooks( 'BeforePageDisplay', array( &$this, &$sk ) );
 
 			wfProfileIn( 'Output-skin' );
 			$sk->outputPage( $this );