shifting bits of ufs/diskd/aufs into libufs.c

(posting from a code-convient place .. :-)

I'm currently trying to neaten up the ufs/aufs/diskd code reuse into a single
file, src/libufs.c (+libufs.h) . The idea here is that most of the code is
actually shared (the directory management stuff particularly), and since I'm
about to implement Yet Another Ufs-type FS as a proof of concept for something
I thought it'd be nice to actually tidy things up.

Attached is a start. I've only modified the diskd code right now - the UFS
and AUFS code should be easily modifyable in a similar fashion and I'll
probably do it to them later this week. My next magic attempt will be to
move over the swaplog routines into libufs.c and make ufs/aufs use it.
The directory rebuild stuff is a little weird though.

Comments? For those who are interested, I'm looking to commit my IFS code
to FreeBSD in the next few days, and so I'm going to make a diskd-ifs
filestore which should be significantly faster than UFS (but again, its
simply a proof of concept for something a little more general. :-)

Adrian

-- 
Adrian Chadd			"The main reason Santa is so jolly is
<adrian@freebsd.org>		   because he knows where all the bad girls
				    live." -- Random IRC quote