Login and Registration: Send `nocache_headers()` on Multisite signup pages.

Props herregroen.
Fixes #43843.
Built from https://develop.svn.wordpress.org/trunk@43030


git-svn-id: http://core.svn.wordpress.org/trunk@42859 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.0-alpha-43027';
+$wp_version = '5.0-alpha-43030';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.

wp-signup.php

@@ -7,6 +7,8 @@ add_action( 'wp_head', 'wp_no_robots' );
 
 require( dirname( __FILE__ ) . '/wp-blog-header.php' );
 
+nocache_headers();
+
 if ( is_array( get_site_option( 'illegal_names' ) ) && isset( $_GET['new'] ) && in_array( $_GET['new'], get_site_option( 'illegal_names' ) ) ) {
 	wp_redirect( network_home_url() );
 	die();