IPv6 Reverse DNS support

  90% development of IPv6 Reverse DNS support with bind.
  Corrected serial stepping to strictly incremental (many servers support only that.)
  Issues, limitations:
	- ipv6 range; dont need it now.
	- would need a correct IPV6 lib, but dont know where / how to place it and
		dont have enough time. Help/instructions needed.
	- ipv6 rev supports netmasking, not here, though. Current implementation
		supports changes only in the last tow nibbles (last byte). So every
		zone is a /112 zone.
Merge pull request #39 from semirke/dev

IPv6 Reverse DNS support