Move frog/leg to lib/compiler/implementation.

frog/frogc.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.
 
 #import('lang.dart', prefix: 'lang');
-#import('leg/frog_leg.dart', prefix: 'leg');
+#import('../lib/compiler/implementation/frog_leg.dart', prefix: 'leg');
 #import('minfrogc.dart', prefix: 'minfrogc');
 
 void main() {
   lang.legCompile = leg.compile;
   try {
     minfrogc.main();
   } catch (var exception, var trace) {
     try {
       print('Internal error: $exception');
     } catch (var ignored) {
       print('Internal error: error while printing exception');
     }
     try {
       print(trace);
     } finally {
       exit(253);
     }
   }
 }