Proxy server cache support

Please, change the code:

function phpch_headers() {
		$expires = get_option( 'phpch_setting', 3600 );

		if ( $expires >= 0 ) {
			header("Pragma: public");
			header("Cache-Control: public, max-age=".$expires);
		} else {
			header("Pragma: no-cache");
			header("Cache-Control: no-cache, max-age=".$expires);
		}

		header('Expires: ' . gmdate('D, d M Y H:i:s', time()+$expires) . ' GMT');
  }

Without public and with must-revalidate proxy server cache doesn’t work. My version work with ISA server cache, ARR cache, IIS cache and do on…

https://wordpress.org/plugins/php-cache-headers/