o Avoid pre-2.5.X mid-layer deadlock due to SCSI malloc fragmentation

For pre-2.5.X kernels, attempt to calculate a safe value
for our S/G list length.  In these kernels, the midlayer
allocates an S/G array dynamically when a command is issued
using SCSI malloc.  This list, which is in an OS dependent
format that must later be copied to our private S/G list, is
sized to house just the number of segments needed for the
current transfer.  Since the code that sizes the SCSI malloc
pool does not take into consideration fragmentation of the
pool, executing transactions numbering just a fraction of our
concurrent transaction limit with list lengths aproaching
AH?_NSEG in length will quickly depleat the SCSI malloc pool
of usable space.

Unfortunately, the mid-layer does not properly handle this
scsi malloc failure.  In kernels prior to 2.4.20, should
the device that experienced the malloc failure be idle and
never have any new I/O initiated (block queue is not "kicked"),
the process will hang indefinitely.  In 2.4.20 and beyond,
the disk experiencing the failure is marked as a "starved
device", but this only helps if I/O is initiated to or completes
on that HBA.  If the failure was induced by another HBA, and
no other I/O is pending on the HBA and no new transactions are
queued, we are still succeptible to the hang.  (Also note that
many 2.4.X kernels do not properly lock the "some_device_starved"
and "device_starved" fields calling into question their overall
effectiveness).

By sizing our S/G list to avoid SCSI malloc pool fragmentation,
we will hopefully avoid this deadlock at least for configurations
where our own HBAs are the only ones using the SCSI subsystem.

 o Correct failed-wait recovery code so that the controller's registers
   will not be accessed without pausing the controller first.

into overdrive.btc.adaptec.com:/usr/home/gibbs/bk/linux-2.5

 o Perform an audit on use of del_timer() and switch to del_timer_sync()
   where appropriate.
 o Remove the reboot notifier hook which is unused in 2.5.X.
 o Correct some driver unload bugs.

 o Correct bus hang on SE->LVD/LVD->SE tranceiver changes
 o Close a race condition in handling bad scsi status that could
   allow the driver to modify the waiting for selection queue while
   selections were enabled.
 o Perform an audit on use of del_timer() and switch to del_timer_sync()
   where appropriate.
 o Remove the reboot notifier hook which is unused in 2.5.X.
 o Correct some driver unload bugs.

to avoid casting problems with different architectures.

magic C promotion to silently do so for us.

was the first file tested with my type checker with the anal
pointer attribute checking turned on.

user space access functions. This allows the type checker
to check proper usage.

checking, these end up being no-ops, but they get enabled
by the type checker as special address_space attributes.

There is a stunning bug.

Previously, it was done automatically by the `reti' isntruction upon
returning from the kernel, but that doesn't do the correct thing in
various cases, for instance if there's a context switch, or a softirq.

Allows for the non standard cascade