[PATCH] Add option to svnserve to disable ipv6

[Jim Morris <mo...@wolfman.com>]

* subversion/svnserve/main.c
   (main): Add --noipv6 option, and if set do not bind to an ipv6 port

On at least one system I am using (OpenBSD) the 1.2.0 version of 
svnserve detects there is an ipv6 network, and binds to that network 
ONLY. So there is no listening port setup on ipv4, so no ipv4 clients 
can connect.

As I do not use ipv6 I added an option --noipv6 which will force it to 
bind to the ipv4 network as previous versions did.

Others with both ipv6 and ipv4 on their systems may encounter similar 
problems as I do not think this is specific to OpenBSD.

Ideally the fix should actually allow it to bind to both ipv6 and ipv4 
networks, however that fix is beyond me at the moment.