Add test

tests/cases/conformance/externalModules/umd9.ts

@@ -0,0 +1,14 @@
+// @module: commonjs
+// @noImplicitReferences: true
+// @allowUmdGlobalAccess: true
+
+// @filename: foo.d.ts
+declare class Thing {
+  foo(): number;
+}
+export = Thing;
+export as namespace Foo;
+
+// @filename: a.ts
+/// <reference path="foo.d.ts" />
+export const x = Foo; // OK in value position because allowUmdGlobalAccess: true