fix fs#2851
related to http://bugs.jqueryui.com/ticket/8761

This should make it possible to see if mod_security is involved,
at least on servers running mod_php.

if a needed CONNECT tunnel fails

Let's stop confusing people with what this button does

Needs a check for null now.

In most cases this change will have no effect, but noes the response will use the filename that was originally requested. The downloaded filename can be modified to something different as well. E.g. the siteexport plugin will make use of it.