Update the protocol buffer compiler plugin to use Int64 from the fixnum package

prepend.dart

Index: prepend.dart
diff --git a/prepend.dart b/prepend.dart
index 1ed9217852d1fe7cce54d3363731554d6cc5c75f..397cfc56aab4ebabaeed2a9c5c2d141cb67a28f6 100755
--- a/prepend.dart
+++ b/prepend.dart
@@ -6,4 +6,7 @@ main() {
   final file = new File(fileName);
   final content = file.readAsStringSync();
   file.writeAsStringSync('#!/usr/bin/env dart\n$content');
+  // For development use the line below instead of the one above to
+  // avoid using the dart2dart code.
+  // file.writeAsStringSync('#!/bin/bash\ndart bin/protoc_plugin.dart');
 }