Fix some hackificator odds and ends in wp-admin:

* `wp-activate.php` and `wp-admin/themes.php` don't need the closing PHP tag
* Switch single quotes for HTML attribute values to double in a few places
* Convert `include_once file.php` syntax to `include_once( 'file.php' )`
* Add access modifiers to methods/members in: `_WP_List_Table_Compat`, `Walker_Nav_Menu_Edit`, `Walker_Nav_Menu_Checklist`, `WP_Screen`, `Walker_Category_Checklist`
* `edit_user()` doesn't need to import the `$wpdb` global
* `wp_list_widgets()` doesn't need to import the `$sidebars_widgets` global
* switch/endswitch syntax is not supported in Hack
* A `<ul>` in `wp-admin/users.php` is unclosed

See #27881.


git-svn-id: https://develop.svn.wordpress.org/trunk@28500 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/revision.php

@@ -126,6 +126,7 @@ function wp_prepare_revisions_for_js( $post, $selected_revision_id, $from = null
 	cache_users( wp_list_pluck( $revisions, 'post_author' ) );
 
 	$can_restore = current_user_can( 'edit_post', $post->ID );
+	$current_id = false;
 
 	foreach ( $revisions as $revision ) {
 		$modified = strtotime( $revision->post_modified );