BUF/BIO cleanup 7/99:

BUF/BIO cleanup 7/99:

First attempt at separating low-level information from BUF structure into
the new BIO structure.  The latter will be used to represent the actual
I/O underlying the buffer cache, other subsystems and device drivers.

Other information from the BUF structure will be moved eventually once
their place in the grand scheme is determined.  For now, preprocess macros
have been added to reduce widespread changes; this is a temporary measure
by all means until more of the BIO and BUF API is formalised.

Remove compatibility preprocessor macros in the AAC driver because our
BUF/BIO system is mutating; not to mention they were getting in the way.

NB the name BIO has been used because it's quite appropriate and known
among kernel developers from other operating system groups, be it BSD or
Linux.

This change should not have any operational affect (famous last words).

Reviewed by:	Matthew Dillon <dillon@dragonflybsd.org>