Update subprocess2.check_output() to behave like subprocess.check_output().

gclient_scm.py

 # Copyright (c) 2011 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Gclient-specific SCM-specific operations."""
 
 import logging
 import os
 import posixpath
 import re
@@ skipping 647 matching lines @@
 
   def _GetCurrentBranch(self):
     # Returns name of current branch or None for detached HEAD
     branch = self._Capture(['rev-parse', '--abbrev-ref=strict', 'HEAD'])
     if branch == 'HEAD':
       return None
     return branch
 
   def _Capture(self, args):
     return subprocess2.check_output(
-        ['git'] + args, cwd=self.checkout_path).strip()
+        ['git'] + args,
+        stderr=subprocess2.PIPE,
+        cwd=self.checkout_path).strip()
 
   def _Run(self, args, options, **kwargs):
     kwargs.setdefault('cwd', self.checkout_path)
     gclient_utils.CheckCallAndFilterAndHeader(['git'] + args,
         always=options.verbose, **kwargs)
 
 
 class SVNWrapper(SCMWrapper):
   """ Wrapper for SVN """
 
@@ skipping 259 matching lines @@
 
     This method returns a new list to be used as a command."""
     new_command = command[:]
     if revision:
       new_command.extend(['--revision', str(revision).strip()])
     # --force was added to 'svn update' in svn 1.5.
     if ((options.force or options.manually_grab_svn_rev) and
         scm.SVN.AssertVersion("1.5")[0]):
       new_command.append('--force')
     return new_command