properly support module imports from within modules.

src/prolog/macros.rs

@@ -783,3 +783,9 @@ macro_rules! set_code_index {
         idx.1 = $mod_name.clone();
     }}
 }
+
+macro_rules! machine_code_index {
+    ($code_dir:expr, $op_dir:expr) => (
+        MachineCodeIndex { code_dir: $code_dir, op_dir: $op_dir }
+    )
+}