bug#20159: 24.4; url-retrieve invokes same callback twice with kill-buffer

[Andy Moreton]

On Fri 27 Mar 2015, Eli Zaretskii wrote:

>> Date: Sun, 22 Mar 2015 19:31:48 +0200
>> From: Eli Zaretskii <eliz@gnu.org>
>> Cc: 20159@debbugs.gnu.org
>> 
>> Due to some subtle technical issues with the 'select' emulation, the
>> ':nowait' subfeature is turned off on Windows since more than 8 years
>> ago.  The result is that the 'connect' call is blocking, and I believe
>> this is what you see.
>> 
>> Volunteers are welcome to add support for non-blocking connections;
>> see these messages for the starting point:
>> 
>>   http://lists.gnu.org/archive/html/emacs-devel/2005-11/msg01586.html
>>   http://lists.gnu.org/archive/html/emacs-devel/2006-12/msg00873.html
>
> No one volunteered, so I did it myself, see commit d133cf8 on master.

This change broke gnus for me on a mingw64 x64 build of emacs, as gnutls
seems unable to connect to the NNTP server at gmane.org.

I will report more details when I have time to investigate this further
with gdb.

    AndyM