Add function for generating validation signatures.

SConstruct

 #! -*- python -*-
 # Copyright (c) 2012 The Native Client Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import atexit
 import glob
 import os
 import platform
 import shutil
@@ skipping 2376 matching lines @@
       'src/trusted/perf_counter/build.scons',
       'src/trusted/platform_qualify/build.scons',
       'src/trusted/plugin/build.scons',
       'src/trusted/python_bindings/build.scons',
       'src/trusted/reverse_service/build.scons',
       'src/trusted/sel_universal/build.scons',
       'src/trusted/service_runtime/build.scons',
       'src/trusted/simple_service/build.scons',
       'src/trusted/threading/build.scons',
       'src/trusted/validator/build.scons',
+      'src/trusted/validator/caching/build.scons',
       'src/trusted/validator/x86/build.scons',
       'src/trusted/validator/x86/decoder/build.scons',
       'src/trusted/validator/x86/decoder/generator/build.scons',
       'src/trusted/validator/x86/ncval_reg_sfi/build.scons',
       'src/trusted/validator/x86/ncval_seg_sfi/build.scons',
       'src/trusted/validator/x86/ncval_seg_sfi/generator/build.scons',
       'src/trusted/validator/x86/32/build.scons',
       'src/trusted/validator/x86/64/build.scons',
       'src/trusted/validator_x86/build.scons',
       'src/trusted/weak_ref/build.scons',
@@ skipping 1395 matching lines @@
   nacl_env.ValidateSdk()
 
 if BROKEN_TEST_COUNT > 0:
   msg = "There are %d broken tests." % BROKEN_TEST_COUNT
   if GetOption('brief_comstr'):
     msg += " Add --verbose to the command line for more information."
   print msg
 
 # separate warnings from actual build output
 Banner('B U I L D - O U T P U T:')