Add regression test.

Author: jseyfried

src/test/run-pass/mod_dir_path.rs

@@ -17,4 +17,15 @@ mod mod_dir_simple {
 
 pub fn main() {
     assert_eq!(mod_dir_simple::syrup::foo(), 10);
+
+    #[path = "auxiliary"]
+    mod foo {
+        mod two_macros;
+    }
+
+    #[path = "auxiliary"]
+    mod bar {
+        macro_rules! m { () => { mod two_macros; } }
+        m!();
+    }
 }