add a new test

tests/cases/compiler/commonSourceDir6.ts

@@ -0,0 +1,17 @@
+// @outFile: concat.js
+// @outDir: a
+// @module: amd
+// @Filename: a/bar.ts
+import {z} from "./foo";
+export var x = z + z;
+
+// @Filename: a/foo.ts
+import {pi} from "../baz";
+export var i = Math.sqrt(-1);
+export var z = pi * pi;
+
+// @Filename: baz.ts
+import {x} from "a/bar";
+import {i} from "a/foo";
+export var pi = Math.PI;
+export var y = x * i;