Fix a few problems with handling rejected transfer negotiation messages.

Use the host message loop for any unknown message types instead of performing
a reject message in the sequencer.  Pass reject messages to the host
message loop too which frees up a sequencer interrupt type slot.

Default to issuing a bus reset if initiator mode is enabled.  It seems
that the reset scsi bus bit is not defined in the same location for
all aic78xx BIOSes, so attempting to honor this setting will have to
wait until I get more information on how to detect it.

Nuke some unused variables.
Don't return stack-based data.  This may have caused
server-side CHAP authentication problems in the past :-/
Sync with sys/i386/isa/fd.c revision 1.129.
Sync with sys/i386/isa/npx.c revision 1.64.
Sync with sys/i386/isa/wd.c revision 1.181.
The fe driver has been merged into sys/i386/isa/if_fe.c.

Forgotten by:	kato
Sync with sys/i386/isa/clock.c revision 1.129.
Add an option for insecure mode, in which rwhod does not discard packets
from incorrect source ports.
Actually document my last addition.
General cosmetics.
Add a note that scsi-defects has not been ported to CAM.
Submitted by:	BDE
Restore old semantics (broken in rev 1.47's buffer overflow fix).
Look for boot blocks in new default location.
Note that dying on NULL is an implementation detail.
Implemented sending of BREAKs.  This is quite complicated because the
hardware is interrupt-driven to a fault and sending a BREAK requires
mode switching.  Always running in the BREAK-capable mode as in PR 8318
would double the overhead for sending \0's.

Reminded by:	PR 8318
Oops, this should have been in the previous commit (ensure atomic update
of com->cor[1]).
Fixed handling of BREAK in input.  BREAK was not being converted into an
escape sequence in the `-ignbrk -brkint parmrk' case.

Found by:	NIST-PCTS
Several changes having to do blocksize- mostly to force variable as the default.
Attempt to determine (at mount time if not done so already) via density code
whether a device should default to fixed mode or not. Attempts to set to
variable that fail will cause fixed to be selected.

Similarly, the '2 filemarks at EOM' quirk is now determined (or attempted to
be determined) via density code. Some as yet not entirely tested code for
coping with 2FM@EOD position is now also in place.
Add some tape specific density codes- only enough of them here to recognize
some specific older units so we can choose 2FM@EOD or FIXED blocksize
quirks.
Flush the tx fifo in cystop().  Now ttyflush() (and thus tcflush(3))
almost works properly.  Unfortunately, there is no way to flush
the rx fifo without resetting the channel, which also flushes the
tx fifo.  We avoid resetting even when both fifos need to be flushed,
since resetting seems to cause the rx to lose sync if it is done
while data is arriving.

Reminded by:	NIST-PCTS
import logical/hardware block locate ioctls from NetBSD
Correct the definition of the changer device capabilities page.  The
previous definition confused some reserved bytes for exchange capabilities.