Rename class AssertError to AssertionError in the VM (fix issue 119).

tests/standalone/src/AssertTest.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.
 // VMOptions=--enable_asserts
 //
 // Dart test program testing assert statements.
 
 class AssertTest {
   static test() {
     int i = 0;
     try {
       assert(false);
-    } catch (AssertError error) {
+    } catch (AssertionError error) {
       i = 1;
       Expect.equals("false", error.failedAssertion);
       int pos = error.url.lastIndexOf("/", error.url.length);
       if (pos == -1) {
         pos = error.url.lastIndexOf("\\", error.url.length);
       }
       String subs = error.url.substring(pos + 1, error.url.length);
       Expect.equals("AssertTest.dart", subs);
       Expect.equals(12, error.line);
       Expect.equals(14, error.column);
     }
     return i;
   }
   static testClosure() {
     int i = 0;
     try {
       assert(() => false);
-    } catch (AssertError error) {
+    } catch (AssertionError error) {
       i = 1;
       Expect.equals("() => false", error.failedAssertion);
       int pos = error.url.lastIndexOf("/", error.url.length);
       if (pos == -1) {
         pos = error.url.lastIndexOf("\\", error.url.length);
       }
       String subs = error.url.substring(pos + 1, error.url.length);
       Expect.equals("AssertTest.dart", subs);
       Expect.equals(30, error.line);
       Expect.equals(14, error.column);
     }
     return i;
   }
 
   static testMain() {
     Expect.equals(1, test());
     Expect.equals(1, testClosure());
   }
 }
 
 main() {
   AssertTest.testMain();
 }