Add support for UMD-like module export format

The new module format enables global-less universal modules,
compatible with both AMD and CJS module loaders.

Fixes #2036.

src/compiler/types.ts

@@ -1671,6 +1671,7 @@ module ts {
         None = 0,
         CommonJS = 1,
         AMD = 2,
+        UMD = 3,
     }
 
     export interface LineAndCharacter {