structural changes should happen, as it now does the right thing
w.r.t. buffer resizing and having lots of buffers vs. relatively
little buffer space. Ports can now "do the standard thing", re:
nbuf and bufpages, which is make nbuf = bufpages by default.
startup in machdep.c... buffers are now *never* allocated after boot.
currently, the limitation that says bufpages must cover nbuf*MAXBSIZE
still exists, but this is one step closer to removing that limitation.