IPv6 support for Pike 7.3 + a new internetworking framework
Imported from http://bugzilla.roxen.com/bugzilla/show_bug.cgi?id=3063
Reported by Marek Habersack, The Caudium Group grendel@caudium.net
The patch implements a generic framework for encompassing and using various address families of the BSD sockets interface. The main reason to implement it was to add the IPv6 support to Pike without losing backwards compatibility.