ensure plugin instantiate can return a module instance

Author: guybedford

lib/register.js

@@ -245,8 +245,8 @@ function createEntry() {
   }
 
   // module binding records
-  function Module() {}
-  defineProperty(Module, 'toString', {
+  function ModuleRecord() {}
+  defineProperty(ModuleRecord, 'toString', {
     value: function() {
       return 'Module';
     }
@@ -256,7 +256,7 @@ function createEntry() {
     return moduleRecords[name] || (moduleRecords[name] = {
       name: name,
       dependencies: [],
-      exports: new Module(), // start from an empty module and extend
+      exports: new ModuleRecord(), // start from an empty module and extend
       importers: []
     });
   }
@@ -416,7 +416,7 @@ function createEntry() {
     exports = module.exports;
 
     // __esModule flag treats as already-named
-    if (exports && exports.__esModule)
+    if (exports && (exports.__esModule || exports instanceof Module))
       entry.esModule = exports;
     // set module as 'default' export, then fake named exports by iterating properties
     else if (entry.esmExports && exports !== __global)