non-ASCII characters in filenames break output formatting

[mgedmin]

Same repository as #23:

$ git clone https://github.com/hhatto/autopep8
$ cd autopep8
$ check-manifest --version
check-manifest version 0.19.dev0
$ check-manifest -u
...
missing from sdist:
  ...
  test/example/é.txt
  ...
suggested MANIFEST.in rules:
  include *.bash
  include *.py
  include *.rst
  include .travis.yml
  include AUTHORS
  include LICENSE
  include Makefile
  include tox.ini
  recursive-include test *.gitignore
  recursive-include test *.py
  recursive-include test *.txt
updating MANIFEST.in
don't know how to come up with rules matching
  hooks/pre-push

and now with the updated MANIFEST.in we get a crash

$ check-manifest
listing source files under version control: 94 files and directories
copying source files to a temporary directory
building an sdist: autopep8-1.0a4.tar.gz: 92 files and directoriesTraceback (most recent call last):
  File "/home/mg/.venv/bin/check-manifest", line 9, in <module>
    load_entry_point('check-manifest==0.19.dev0', 'console_scripts', 'check-manifest')()
  File "/home/mg/src/check-manifest/check_manifest.py", line 658, in main
    update=args.update, python=args.python):
  File "/home/mg/src/check-manifest/check_manifest.py", line 594, in check_manifest
    "VCS", "sdist"))
  File "/home/mg/src/check-manifest/check_manifest.py", line 117, in format_difference
    return '\n'.join(res)
UnicodeDecodeError: 'ascii' codec can't decode byte 0xcc in position 34: ordinal not in range(128)

[mgedmin]

This would be because source_files is a list of Unicode filenames including

 u'test/example/e\u0301.py',
 u'test/example/e\u0301.txt',

while sdist_files is a list of bytestrings including

 'test/example/e\xcc\x81.py',
 'test/example/e\xcc\x81.txt',

[mgedmin]

Hey, check-manifest works fine on this repository if I use Python 3 ;)