Fix for do/while: if there are phi copies after the condition, emit the non-pretty while loop.

tests/language/do_while2_test.dart

+// Copyright (c) 2012, 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.
+
+var a = 42;
+
+foo1() {
+  var i = 0;
+  var saved;
+  do {
+    saved = i;
+    i = a;
+  } while (i == saved);
+  Expect.equals(0, saved);
+  Expect.equals(42, i);
+}
+
+foo2() {
+  var i = 0;
+  var saved;
+  do {
+    saved = i;
+    i = a;
+  } while (i != saved);
+  Expect.equals(42, saved);
+  Expect.equals(42, i);
+}
+
+foo3() {
+  var i = 0;
+  var saved;
+  do {
+    saved = i;
+    i = a;
+    if (i == saved) continue;
+  } while (i != saved);
+  Expect.equals(42, saved);
+  Expect.equals(42, i);
+}
+
+main() {
+  foo1();
+  foo2();
+  foo3();
+}