Add fmt_xlong function support

fmt_xlong.c is extracted from http://www.fefe.de/dns/djbdns-1.05-test25.diff.bz2

Visit http://www.fefe.de/dns/ for more information.

Signed-off-by: Giam Teck Choon <giamteckchoon@gmail.com>
Add ip6_scan, ip6_scan_flat, ip6_fmt and ip6_fmt_flat functions

Copy and modify from fefe's djbdns IPv6 patch:

http://www.fefe.de/dns/djbdns-1.05-test25.diff.bz2

Mainly from ip6.h into ip.h, ip6_scan.c and ip6_fmt.c into ip.c

See http://www.fefe.de/dns/

Signed-off-by: Giam Teck Choon <giamteckchoon@gmail.com>