Add a snapshot for docgen and use it in the build

sdk/bin/docgen.bat

Index: sdk/bin/docgen.bat
diff --git a/sdk/bin/dartdoc.bat b/sdk/bin/docgen.bat
similarity index 90%
copy from sdk/bin/dartdoc.bat
copy to sdk/bin/docgen.bat
index c80ef9540a12138d9ebabb3a1ea037f4167652b9..061757b62db69994006136ced0e0d58d100c7845 100644
--- a/sdk/bin/dartdoc.bat
+++ b/sdk/bin/docgen.bat
@@ -1,5 +1,5 @@
 @echo off
-REM Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+REM Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 REM for details. All rights reserved. Use of this source code is governed by a
 REM BSD-style license that can be found in the LICENSE file.
 
@@ -17,7 +17,7 @@ for %%i in ("%BIN_DIR%\..\") do set SDK_DIR=%%~fi
 rem Remove trailing backslash if there is one
 IF %SDK_DIR:~-1%==\ set SDK_DIR=%SDK_DIR:~0,-1%
 
-set DARTDOC=%SDK_DIR%\lib\_internal\dartdoc\bin\dartdoc.dart
+set DOCGEN=%SDK_DIR%\pkg\docgen\bin\docgen.dart
 set DART=%BIN_DIR%\dart
 set SNAPSHOT=%BIN_DIR%\snapshots\utils_wrapper.dart.snapshot
 
@@ -29,7 +29,7 @@ if exist "%SNAPSHOT%" (
 ) else (
   :: The trailing forward slash in --package-root is required because of issue
   :: 9499.

[ricow1, 2014/01/13 13:14:20]

I am not sure this is valid anymore

[Alan Knight, 2014/01/13 17:36:04]

It doesn't seem to be. Removed here and from the dartdoc.bat script.

-  "%BUILD_DIR%\dart-sdk\bin\dart" "--package-root=%BUILD_DIR%\packages/" "%DARTDOC%" %*
+  "%BUILD_DIR%\dart-sdk\bin\dart" "--package-root=%BUILD_DIR%\packages/" "%DOCGEN%" %*
 )
 
 endlocal