[BUG] svn 1.2.x cannot reach dual-stack svnserve with IPv4

        Hello,

As of version 1.2.0, the svn client tries to connect to svnserve over
IPv6 if it is advertised in the DNS. However, the client fails to
fallback properly to IPv4 when IPv6 is not available.

I'm using these :
Subversion 1.2.0
APR 2.0.54
Neon 0.24.7

Admittedly not the most recent versions, but there's no mention ipv6 in
the ChangeLog for 1.2.1.

The problem can easily be reproduced as follow :

basile.via.ecp.fr is a dual-stack server running svnserve :
basile.via.ecp.fr has IPv6 address 2002:8ac3:802d:1242:250:4ff:fe4c:ae54
basile.via.ecp.fr has address 138.195.157.222

On an IPv6-only host or dual-stack host, everything works fine :

% svn ls svn://basile.via.ecp.fr/miredo
branches/
tags/
trunk/

However, on an dual-stack host with *no* IPv6 connectivity, it fails :

% svn ls svn://basile.via.ecp.fr/miredo
svn: Can't connect to host 'basile.via.ecp.fr': Network is unreachable

It works fine with subversion 1.0.x. Correct semantic for dual-stack
client programs trying to contact dual-stack servers consists of trying
to use IPv6 and then IPv4 if IPv6 fails. svn doesn't try IPv4.

As a consequence, it is not possible to use svn 1.2.x from IPv4-only
hosts to reach dual-stack servers.

-- 
Rémi Denis-Courmont
http://www.simphalempin.com/home/