Small tweak for random read performance (we shouldn't always tell the OS that...

Small tweak for random read performance (we shouldn't always tell the OS that we will be doing a linear scan). 

sql/examples/ha_tina.cc

@@ -609,7 +609,8 @@ int ha_tina::rnd_init(bool scan)
   records= 0;
   chain_ptr= chain;
 #ifdef HAVE_MADVISE
-  (void)madvise(share->mapped_file,share->file_stat.st_size,MADV_SEQUENTIAL);
+  if (scan)
+    (void)madvise(share->mapped_file,share->file_stat.st_size,MADV_SEQUENTIAL);
 #endif
 
   DBUG_RETURN(0);