Admin: allow `WP_Screen` to be checked via autoload in `convert_to_screen()`.

Props kraftbj.
See #36335.

Built from https://develop.svn.wordpress.org/trunk@38414


git-svn-id: http://core.svn.wordpress.org/trunk@38355 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/template.php

@@ -1989,7 +1989,7 @@ function _wp_admin_html_begin() {
  * @return WP_Screen Screen object.
  */
 function convert_to_screen( $hook_name ) {
-	if ( ! class_exists( 'WP_Screen', false ) ) {
+	if ( ! class_exists( 'WP_Screen' ) ) {
 		_doing_it_wrong( 'convert_to_screen(), add_meta_box()', __( "Likely direct inclusion of wp-admin/includes/template.php in order to use add_meta_box(). This is very wrong. Hook the add_meta_box() call into the add_meta_boxes action instead." ), '3.3.0' );
 		return (object) array( 'id' => '_invalid', 'base' => '_are_belong_to_us' );
 	}

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.7-alpha-38413';
+$wp_version = '4.7-alpha-38414';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.