Updated cross-platform IPv6 support

[Bryan O'Sullivan]

Bryan O'Sullivan wrote:

> Here's a patch that should be more portable.  It gets rid of all mention 
> of s6_addr32, fixes a broken autoconf test, and adds some more AI_* 
> flags that are required for correct functioning on some platforms (e.g. 
> recent Linux/glibc).

I've had a chance to test it out on OS X.  It required a little more 
tweaking, but now works nicely.  The same code also works on Fedora 7 
and Debian Etch.

You can get the results here:

darcs get --partial http://darcs.serpentine.com/network

	<b