SCSI device removal fixes

Fix a few issues related to SCSI device removal:
- Fix a race between starved list processing and device removal that can trigger a kernel oops.
- Avoid that __scsi_remove_device() is called twice for the same SCSI device, which also can cause a kernel oops.
- Restrict the SCSI device state changes allowed via sysfs.
- Avoid re-enabling I/O after the transport layer became offline.

Changes compared to v13:
- Reworked the patch for avoiding to re-enable I/O while removing an offline device by introducing a new SCSI device state (SDEV_CANCEL_OFFLINE).

Changes compared to v12:
- Clarified the description of the patch for handling a transport layer failure during LUN scanning: mentioned that this patch was developed after analyzing the cause of a kernel oops triggered by asynchronous LUN scanning.
- Restored the previous version of the patch for restricting sysfs SCSI device state changes, namely the version that only disallows changing the device state into "cancel" or "deleted".
- Added a comment in patch 4/4.
- Left out a patch that was the result of source reading and also an intermediate patch that is no longer needed in this series.

Changes compared to v11:
- Left out a patch that was not a device removal bug fix.
- Left out the patches about which there is not yet an agreement.

Changes compared to v10:
- Rebased and retested on top of Linux kernel v3.10-rc5.

Changes compared to v9:
- Changed one WARN_ON() statement into a WARN() statement.

Changes compared to v8:
- Addressed the feedback from Joe Lawrence - dropped the patch that makes scsi_remove_host() wait until the last sdev user is gone.
- Eliminated Scsi_Host.tmf_in_progress since it duplicates state information available in Scsi_Host.eh_active.
- Added a patch to avoid reenabling I/O after the transport layer became offline.

Changes compared to v7:
- Addressed the review comments posted by Hannes Reinecke and Rolf Eike Beer.
- Modified patch "Make scsi_remove_host() wait until error handling finished" such that it is also safe for SCSI timeout values below the maximum LLD response time by modifying scsi_send_eh_cmnd() such that it does not invoke any LLD code after scsi_remove_host() started.
- Added a patch to save and restore the host_scribble field.
- Refined / clarified several patch descriptions.
- Rebased and retested on top of kernel v3.8-rc6.

Changes compared to v6:
- Dropped the first six patches since Jens queued these for 3.8.
- Added patch to avoid that __scsi_remove_device() is invoked twice.
- Restore error recovery in the SHOST_CANCEL state.

Changes compared to v5:
- Avoid that block layer work can be scheduled on a dead queue.
- Do not invoke any SCSI LLD callback after scsi_remove_host() finished.
- Stop error handling as soon as scsi_remove_host() started.
- Remove the unused function bsg_goose_queue().
- Avoid that scsi_device_set_state() triggers a race condition.

Changes compared to v4:
- Moved queue_flag_set(QUEUE_FLAG_DEAD, q) from blk_drain_queue() into blk_cleanup_queue().
- Declared the new __blk_run_queue_uncond() function inline. Checked in the generated assembler code that this function is really inlined in __blk_run_queue().
- Elaborated several patch descriptions.
- Added sparse annotations to scsi_request_fn().
- Split several patches.

Changes compared to v3:
- Fixed a race condition by setting QUEUE_FLAG_DEAD earlier.
- Added a patch for fixing a race between starved list processing and device removal to this series.

Changes compared to v2:
- Split second patch into two patches.
- Refined patch descriptions.

Changes compared to v1:
- Included a patch to rename QUEUE_FLAG_DEAD.
- Refined the descriptions of the __blk_run_queue_uncond() and blk_cleanup_queue() functions.