print error on stderr

src/chunk_manager.c

@@ -10,7 +10,7 @@ void chunk_merge(chunk_t *first, chunk_t *second)
 {
 #ifndef DEBUG
     if (first->block_id != second->block_id)
-        putstr("Attempt merge two chunk on different block\n");
+        write(2, "Attempt merge two chunk on different block\n", 43);
 #endif        
 	first->size = second->data_start - first->data_start + second->size;
 	first->next = second->next;