When verify fails, dump the good/bad blocks to files

This makes it easy to compare afterwards to see what kind of
corruption was experienced.

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/lib/rand.h b/lib/rand.h
index 573116c..02e6858 100644
--- a/lib/rand.h
+++ b/lib/rand.h
@@ -19,6 +19,7 @@
 }
 
 extern void init_rand(struct frand_state *);
-extern void fill_random_buf(void *buf, unsigned int len);
+extern void __fill_random_buf(void *buf, unsigned int len, unsigned long seed);
+extern unsigned long fill_random_buf(void *buf, unsigned int len);
 
 #endif