Roll version of gsutil to 4.15.

third_party/gsutil/gslib/addlhelp/crc32c.py

 # -*- coding: utf-8 -*-
 # Copyright 2013 Google Inc. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
 # You may obtain a copy of the License at
 #
 #     http://www.apache.org/licenses/LICENSE-2.0
 #
 # Unless required by applicable law or agreed to in writing, software
@@ skipping 92 matching lines @@
 
   Windows
   -------
 
   An installer is available for the compiled version of crcmod from the Python
   Package Index (PyPi) at the following URL:
 
   https://pypi.python.org/pypi/crcmod/1.7
 
   MSI installers are available for the 32-bit versions of Python 2.6 and 2.7.
+  Make sure to install to a 32-bit Python directory. If you're using 64-bit
+  Python it won't work with 32-bit crcmod, and instead you'll need to install
+  32-bit Python in order to use crcmod.
 
+  Note: If you have installed crcmod and gsutil hasn't detected it, it may have
+  been installed to the wrong directory. It should be located at
+  <python_dir>\\files\\Lib\\site-packages\\crcmod\\
+
+  In some cases the installer will incorrectly install to
+  <python_dir>\\Lib\\site-packages\\crcmod\\
+
+  Manually copying the crcmod directory to the correct location should resolve
+  the issue.
 """)
 
 
 class CommandOptions(HelpProvider):
   """Additional help about CRC32C and installing crcmod."""
 
   # Help specification. See help_provider.py for documentation.
   help_spec = HelpProvider.HelpSpec(
       help_name='crc32c',
       help_name_aliases=['crc32', 'crc', 'crcmod'],
       help_type='additional_help',
       help_one_line_summary='CRC32C and Installing crcmod',
       help_text=_DETAILED_HELP_TEXT,
       subcommand_help_text={},
   )