The core scsi target lib functions.

TODO:
- mv md/dm-bio-list.h to linux/bio-list.h so md and us do not have to
do that weird include.
- convert scsi_tgt_cmd's work struct to James's execute code. And try
to kill our scsi_tgt_cmd.
- add host state checking. We do refcouting so hotplug is partially
supported, but we need to add state checking to make it easier on
the LLD.
Signed-off-by: NMike Christie <michaelc@cs.wisc.edu>
Signed-off-by: NFUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: NJames Bottomley <James.Bottomley@SteelEye.com>