twa(4) support for smartmontools

[Jung-uk Kim]

I added twa(4) support for ports/sysutils/smartmontools.  If you have 
one of those supported controllers, please test and let me know.

http://people.freebsd.org/~jkim/smartmontools-port.tgz

It's lightly tested on -CURRENT/amd64.  If you have twe(4), I'd like 
to hear about it also because I may have broken twe(4) support.

For example, the following command will give you all SMART info for a 
disk on third port of first controller, which is `/c0/p2' in 
tw_cli(8) syntax.

	smartctl -a -d 3ware,2 /dev/twa0

I believe twe(4) is similar, i. e.,

	smartctl -a -d 3ware,2 /dev/twed0

Thanks,

Jung-uk Kim