[BLOCK] Add request_queue_t and mark it deprecated

Andrew thinks I should be nice and allow outside code to at least just
compile, so add the request_queue_t typedef back and mark it deprecated.
It'll warn people that this type is going away soonish.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

include/linux/blkdev.h

@@ -37,6 +37,7 @@
 struct scsi_ioctl_command;
 
 struct request_queue;
+typedef struct request_queue request_queue_t __deprecated;
 struct elevator_queue;
 typedef struct elevator_queue elevator_t;
 struct request_pm_state;