Typo fix. Props paul@byte. fixes #7323 for 2.6

git-svn-id: http://svn.automattic.com/wordpress/branches/2.6@8346 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/edit-pages.php

@@ -122,7 +122,7 @@
 $pagenum = absint( $_GET['pagenum'] );
 if ( empty($pagenum) )
 	$pagenum = 1;
-if( !$per_page || $pre_page < 0 )
+if( !$per_page || $per_page < 0 )
 	$per_page = 20;
 
 $num_pages = ceil(count($posts) / $per_page);