[Dillo-dev] abort failed queries

I wanted to inform the user when a query failed by showing a message and greying out the stop icon instead of letting them wait forever and wonder. Patch attached. Examples: starurchin.org (Connection refused at present, anyway. Fails immediately.) auriga.wearlab.de (no server there, of course. Takes a minute or so.) dillo.asdfgh (leaves the DNS error msgs alone and greys the stop icon.)