Mark mandatory elevator functions in the biodoc.txt

				results in some sort of conflict internally,

				this hook allows it to do that.

elevator_dispatch_fn		fills the dispatch queue with ready requests.

elevator_dispatch_fn*		fills the dispatch queue with ready requests.

				I/O schedulers are free to postpone requests by

				not filling the dispatch queue unless @force

				is non-zero.  Once dispatched, I/O schedulers

				are not allowed to manipulate the requests -

				they belong to generic dispatch queue.

elevator_add_req_fn		called to add a new request into the scheduler

elevator_add_req_fn*		called to add a new request into the scheduler

elevator_queue_empty_fn		returns true if the merge queue is empty.

				Drivers shouldn't use this, but rather check

elevator_deactivate_req_fn	Called when device driver decides to delay

				a request by requeueing it.

elevator_init_fn

elevator_init_fn*

elevator_exit_fn		Allocate and free any elevator specific storage

				for a queue.