Make check_output of subprocess2 compatible with Python's subprocess.

subprocess2.py

 # coding=utf8
 # Copyright (c) 2012 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.
 """Collection of subprocess wrapper functions.
 
 In theory you shouldn't need anything else in subprocess, or this module failed.
 """
 
 import cStringIO
@@ skipping 16 matching lines @@
 TIMED_OUT = -2001
 
 # Globals.
 # Set to True if you somehow need to disable this hack.
 SUBPROCESS_CLEANUP_HACKED = False
 
 
 class CalledProcessError(subprocess.CalledProcessError):
   """Augment the standard exception with more data."""
   def __init__(self, returncode, cmd, cwd, stdout, stderr):
-    super(CalledProcessError, self).__init__(returncode, cmd)
-    self.stdout = stdout
+    super(CalledProcessError, self).__init__(returncode, cmd, output=stdout)
+    self.stdout = self.output  # for backward compatibility.
     self.stderr = stderr
     self.cwd = cwd
 
   def __str__(self):
     out = 'Command %s returned non-zero exit status %s' % (
         ' '.join(self.cmd), self.returncode)
     if self.cwd:
       out += ' in ' + self.cwd
     return '\n'.join(filter(None, (out, self.stdout, self.stderr)))
 
@@ skipping 457 matching lines @@
 
   - Throws if return code is not 0.
   - Works even prior to python 2.7.
   - Blocks stdin by default if not specified since no output will be visible.
   - As per doc, "The stdout argument is not allowed as it is used internally."
   """
   kwargs.setdefault('stdin', VOID)
   if 'stdout' in kwargs:
     raise ValueError('stdout argument not allowed, it would be overridden.')
   return check_call_out(args, stdout=PIPE, **kwargs)[0]