prohibit use of both define() and module.setExports() at the same time

packages/api-utils/lib/securable-module.js

@@ -291,6 +291,12 @@
                   careful to leave self.modules[path] alone, as it will have
                   been modified in the asyncMain() callback-handling code,
                   fired during sandbox.evaluate(). */
+               if (self.defineUsed[path]) {
+                   // you can do one or the other, not both
+                   throw new Error("define() was used, so module.exports= and "
+                                   + "module.setExports() may not be used: "
+                                   + path);
+               }
                self.modules[path] = posteval_exports;
              }
            }

packages/api-utils/tests/modules/dupeSetExports.js

@@ -0,0 +1,4 @@
+define({name: "dupeSetExports"});
+
+// so this should cause a failure
+module.setExports("no no no");

packages/api-utils/tests/test-set-exports.js

@@ -8,6 +8,16 @@ exports.testSetExports = function(test) {
   test.assertEqual(five, 5);
 }
 
+exports.testDupeSetExports = function(test) {
+  var passed = false;
+  try {
+    var dupe = require('modules/dupeSetExports');
+  } catch(e) {
+    passed = /define\(\) was used, so module\.exports= and module\.setExports\(\) may not be used/.test(e.toString());
+  }
+  test.assertEqual(passed, true, 'define() or setExports(), not both');
+}
+
 exports.testModule = function(test) {
   // module.id is not cast in stone yet. For now, it's just the module name.
   // In the future, it may include the package name too, or may possibly be a