modular kernconf

[Buganini]

I've made a patch to allow using section/nosection in kernconf.
http://140.112.64.5/buganini/config.patch

My uname -a:
FreeBSD Zeta.twbbs.org 8.0-CURRENT FreeBSD 8.0-CURRENT #9: Fri Feb 20
01:18:21 CST 2009     root at Zeta.twbbs.org:/usr/obj/usr/src/sys/ZETA
i386

Currently this patch can deal with cpu/options/device/makeoptions,
probably enough (actually I think options/device is usually enough).

I havent tested it fully, just modify GENERIC as follow:
...
section         USB2
# USB core support
...
section         FireWire
# FireWire support
...

and the customized kernconf:
include         GENERIC
ident            ZETA
nosection     USB2
nosection     FireWire

then `config ZETA`,
I can see corresponding in
/usr/src/sys/i386/compile/ZETA/config.c

The default section is "main", everythins before the first section
direction will be in section "main".
I've not really make kernel by this yet.