As discussed in a thread on this list titled:
    "RFC: short reads on block devices"
this patch provides additional information associated
with a medium error. And that is that the data-in buffer
contains no valid data.

This patch is against lk 2.6.36

Changelog:
    set resid to the requested data-in length when a
    MEDIUM ERROR is simulated. This implies no valid
    data is returned in the data-in buffer

Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>