multicast abilities depending on definedness of symbols and use hard-wired
system-dependent configuration defines instead.
Please test whereever you can.
The changes are just too extensive for lazy me to list them
there, but see the comment at the top of sysdep/unix/krt.c.
The code got a bit more ifdeffy than I'd like, though.
Also fixed a bunch of FIXME's and added a couple of others. :)
documented the remaining ones (sysdep/cf/README).
Available configurations:
o linux-20: Old Linux interface via /proc/net/route (selected by default
on pre-2.1 kernels).
o linux-21: Old Linux interface, but device routes handled by the
kernel (selected by default for 2.1 and newer kernels).
o linux-22: Linux with Netlink (I play with it a lot yet, so it isn't
a default).
o linux-ipv6: Prototype config for IPv6 on Linux. Not functional yet.
