Allow underscores in DNS names

[Barry Pederson]

Dan Nelson wrote:
> In the last episode (Mar 29), Dag-Erling Smorgrav said:
> 
>>The attached patch, inspired by a discussion on -STABLE, modifies our
>>resolver library to allow underscores in host names, by classifying
>>the underscore as a hyphen character.  Even though RFC952 forbids
>>them, underscores are becoming increasingly common in DNS, and they
>>are sometimes used for mechanisms (such as Microsoft's automatic proxy
>>configuration scheme) which we might want to support in FreeBSD.
> 
> 
> I thought proxy autodetect used wpad.domainname.com or looked up
> http://domainname.com/wpad.dat ?  All the XP machines here do that.

The underscore in DNS names is showing up in things like RFC2872 (A DNS RR 
for specifying the location of services), and "DNS-based Service discovery" 
as found in Zeroconf/Rendezvous.

     Barry