Initial blktrace support

This doesn't work yet, just committing what little bits I did as not
to lose them.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fio.h b/fio.h
index 060a1ee..d0506f9 100644
--- a/fio.h
+++ b/fio.h
@@ -826,6 +826,12 @@
 extern void td_io_close_file(struct thread_data *, struct fio_file *);
 
 /*
+ * blktrace support
+ */
+extern int is_blktrace(const char *);
+extern int load_blktrace(struct thread_data *, const char *);
+
+/*
  * If logging output to a file, stderr should go to both stderr and f_err
  */
 #define log_err(args...)	do {		\