[PATCH] scsi disk (sd) driver 2.5.12

This patch has the last bit of Justin Gibb's patch
described in:
http://marc.theaimsgroup.com/?l=linux-scsi&m=101200279101550&w=2
[this bit for the sd driver]

There is also a major code cleanup of the sd driver with
documentation headers added and a few obvious bugs fixed
described in:
http://marc.theaimsgroup.com/?l=linux-scsi&m=101798201714399&w=2
I did this cleanup.

Justin's patch has been in Dave's tree for several months while
my code cleanup patch has been there since 2.5.9-dj1 .