Add support for bs_is_seq_rand

This option will switch the meaning of the read,write part of any
blocksize setting to mean sequential,random instead.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/thread_options.h b/thread_options.h
index 32677e2..eaafaee 100644
--- a/thread_options.h
+++ b/thread_options.h
@@ -105,6 +105,7 @@
 	unsigned int softrandommap;
 	unsigned int bs_unaligned;
 	unsigned int fsync_on_close;
+	unsigned int bs_is_seq_rand;
 
 	unsigned int random_distribution;
 
@@ -317,6 +318,7 @@
 	uint32_t softrandommap;
 	uint32_t bs_unaligned;
 	uint32_t fsync_on_close;
+	uint32_t bs_is_seq_rand;
 
 	uint32_t random_distribution;
 	fio_fp64_t zipf_theta;