Add --debug for enabling internal dumps on various actions

A little weak currently, when it's fully integrated everywhere in
fio it'll help find fio problems that I can't trigger.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/log.c b/log.c
index 039e74b..5b21ee2 100644
--- a/log.c
+++ b/log.c
@@ -84,6 +84,9 @@
 		io_u->file = &td->files[ipo->fileno];
 		get_file(io_u->file);
 
+		dprint(FD_IO, "iolog: get %llu/%lu/%s\n", io_u->offset,
+					io_u->buflen, io_u->file->file_name);
+
 		if (ipo->delay)
 			iolog_delay(td, ipo->delay);