This patch against a recent bk 2.6 changes scsi_cmd_ioctl to take a
gendisk as an argument instead of a request_queue_t. This allows scsi char
devices to use the scsi_cmd_ioctl interface.

In turn, change bio_map_user to also pass a request_queue_t, and add a
__bio_add_page helper that takes a request_queue_t.

Tested ide cd burning with no problems.

If the scsi upper level scsi_cmd_ioctl usage were consolidated in
scsi_prep_fn, we could pass a request_queue_t instead of a gendisk to
scsi_cmd_ioctl.