scsi error handler improvements

Hello,

over the last year we had an endless number of issues with hard raid units from various vendors. Due this we also have been running into problems with the scsi error handler.

This is just as before, but without the first two patches ("print eh activation" and "Allow requeuement on DID_SOFT_ERROR").

Thanks,
Bernd

Bernd Schubert
Q-Leap Networks GmbH