don't allow blog sub site in folder install, see #13304

git-svn-id: http://svn.automattic.com/wordpress/trunk@14516 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/schema.php

@@ -710,6 +710,8 @@ Thanks!
 		'subdomain_install' => intval( $subdomain_install ),
 		'global_terms_enabled' => global_terms_enabled() ? '1' : '0'
 	);
+	if ( !intval( $subdomain_install ) ) 
+		$sitemeta['illegal_names'][] = 'blog';
 
 	$insert = '';
 	foreach ( $sitemeta as $meta_key => $meta_value ) {