Proper heading for admin screens.

First step towards restoring a good heading structure in wp-admin.
The previous `<h1>` contained the site title and a link to the front page and was removed with the toolbar refactoring in 3.2.

Props joedolson, afercia.
Fixes #31650.



git-svn-id: https://develop.svn.wordpress.org/trunk@32974 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/export.php

@@ -143,7 +143,7 @@ function export_date_options( $post_type = 'post' ) {
 ?>
 
 <div class="wrap">
-<h2><?php echo esc_html( $title ); ?></h2>
+<h1><?php echo esc_html( $title ); ?></h1>
 
 <p><?php _e('When you click the button below WordPress will create an XML file for you to save to your computer.'); ?></p>
 <p><?php _e('This format, which we call WordPress eXtended RSS or WXR, will contain your posts, pages, comments, custom fields, categories, and tags.'); ?></p>