const enums, iteration 1: const enums can be used in imports, const enums can be merged only with const enums.

src/compiler/commandLineParser.ts

@@ -118,6 +118,10 @@ module ts {
             shortName: "w",
             type: "boolean",
             description: Diagnostics.Watch_input_files,
+        },
+        {
+            name: "preserveConstEnums",
+            type: "boolean"
         }
     ];