Updates the IIS web.config file with the current rules if it is writable.

If the permalinks do not require rewrite rules then the rules are deleted from the web.config file.

function iis7_save_url_rewrite_rules() {
	global $wp_rewrite;

	if ( is_multisite() ) {
		return;
	}

	// Ensure get_home_path() is declared.
	require_once ABSPATH . 'wp-admin/includes/file.php';

	$home_path       = get_home_path();
	$web_config_file = $home_path . 'web.config';

	// Using win_is_writable() instead of is_writable() because of a bug in Windows PHP.
	if ( iis7_supports_permalinks()
		&& ( ! file_exists( $web_config_file ) && win_is_writable( $home_path ) && $wp_rewrite->using_mod_rewrite_permalinks()
			|| win_is_writable( $web_config_file ) )
	) {
		$rule = $wp_rewrite->iis7_url_rewrite_rules( false );

		if ( ! empty( $rule ) ) {
			return iis7_add_rewrite_rule( $web_config_file, $rule );
		} else {
			return iis7_delete_rewrite_rule( $web_config_file );
		}
	}

	return false;
}