[PATCH] sg.c: update

The attachment combines the most recent patch from
Yum Rayan <yum.rayan@gmail.com> (to reduce sg stack
usage), Adrian Bunk <bunk@stusta.de> (to fix check
after use) and me (fix elapsed time calculation
(duration) on ia64 machines).

I have modified the patch from Yum Rayan so kmalloc()
in sg_read() is only called for the (rare) code paths
that need them.

Changelog:
   - reduce stack usage in sg_ioctl() and sg_read()
   - fix check after use in sg_mmap()
   - hold duration internally in milliseconds and
     check current time later than held time

Signed-off-by: Douglas Gilbert <dougg@torque.net>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>