Branch b1_8_gate

b=12755,16494,16404
i=bzzz
i=adilger

several fixes in the sd_iostat patch:
- remove the limit of 256 scsi disks
- unloading/reloading the scsi low level driver triggers a kernel
  bug when trying to access the sd iostat file.
- REQ_BLOCK_PC requests are not handled properly causing memory corruption.