[amd64] reusing FreeBSD code

[Jordan Gordeev]

Hi!
I'm the GSoC student doing the amd64 port.
About the status of my project: I'm so much behind schedule, that I'd 
better not think about it.
As is just natural, instead of reinventing the wheel, while doing my 
project, I can borrow a lot of code from FreeBSD.
I'd like to here your advice on the following:
1) which FreeBSD code can be reused
2) which FreeBSD code should be reused
3) which FreeBSD code should *not* be reused, i.e. it's better if 
DragonFly gets some from-scratch implementation, rather than using 
FreeBSD code