Dartc was not raising an error if an interface declared constructors without a default clause

tests/stub-generator/src/MintMakerPromiseWithStubsTest.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // IsolateStubs=MintMakerPromiseWithStubsTest.dart:Mint,Purse
 
 #library("MintMakerPromiseWithStubsTest-generatedTest");
 #import("../../isolate/src/TestFramework.dart");
 
 interface Mint default MintImpl {
@@ skipping 81 matching lines @@
 
     // FIXME(benl): We should not have to manually order the calls
     // like this.
     Promise<int> result = sprouted.deposit(5, purse);
     Promise p1 = expect.completesWithValue(result, 5);
     Promise<bool> p2 = new Promise<bool>();
     Promise<bool> p3 = new Promise<bool>();
     Promise<bool> p4 = new Promise<bool>();
     Promise<bool> p5 = new Promise<bool>();
     Promise<bool> p6 = new Promise<bool>();
-    result.addCompleteHandler((_) {
+    result.addCompleteHandler((unused) {
       expect.completesWithValue(sprouted.queryBalance(), 0 + 5)
-        .then((_) => p2.complete(true));
+        .then((unused_) => p2.complete(true));
       expect.completesWithValue(purse.queryBalance(), 100 - 5)
-        .then((_) => p3.complete(true));
+        .then((unused_) => p3.complete(true));
 
       result = sprouted.deposit(42, purse);
-      expect.completesWithValue(result, 5 + 42).then((_) => p4.complete(true));
-      result.addCompleteHandler((_) {
+      expect.completesWithValue(result, 5 + 42).then((unused__) => p4.complete(true));
+      result.addCompleteHandler((unused_) {
         expect.completesWithValue(sprouted.queryBalance(), 0 + 5 + 42)
-          .then((_) => p5.complete(true));
+          .then((unused___) => p5.complete(true));
         expect.completesWithValue(purse.queryBalance(), 100 - 5 - 42)
-          .then((_) => p6.complete(true));
+          .then((unused___) => p6.complete(true));
         });
     });
     Promise<bool> done = new Promise<bool>();
     done.waitFor([p1, p2, p3, p4, p5, p6], 6);
     done.then((_) {
       expect.succeeded();
       print("##DONE##");
     });
   }
 
 }
 
 main() {
   runTests([MintMakerPromiseWithStubsTest.testMain]);
 }