Set default IO scheduler to ROW and merge block&ROW improvements

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block: Add support for reinsert a dispatched req
block: Add API for urgent request handling
row: Adding support for reinsert already dispatched req
row: Add support for urgent request handling
block: row: Add some debug information on ROW queues
block: row: Insert dispatch_quantum into struct row_queue
block: row: fix sysfs functions - idle_time conversion
block: row: Aggregate row_queue parameters to one structure

Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
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iosched: prevent aliased requests from starving other I/O

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
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block: reorganize queue draining
block: reorder elevator switch sequence
block: remove elevator_queue->ops

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Change-Id: If21a8cd2de9a3257de072326ff55cab87b6c1536