Py3 compat.

[mikewaters]

Two small python 3 issues:

• subprocess.Popen returns command output as bytestring, not string
• Exceptions have no 'message' attribute

Fixes tested on python 3.4.2/linux.

[mikewaters]

Example of error:

worker_8 | [2015-03-21 19:41:46,526: DEBUG/Worker-8] running installed command ['flake8-diff', 'origin/master']
worker_8 | Traceback (most recent call last):
worker_8 |   File "/tmp/python_workspace-command-flake8_diff-43ff8293/env/lib/python3.4/site-packages/flake8diff/main.py", line 130, in main
worker_8 |     ).process()
worker_8 |   File "/tmp/python_workspace-command-flake8_diff-43ff8293/env/lib/python3.4/site-packages/flake8diff/flake8.py", line 157, in process
worker_8 |     for filename in vcs.changed_files():
worker_8 |   File "/tmp/python_workspace-command-flake8_diff-43ff8293/env/lib/python3.4/site-packages/flake8diff/vcs/git.py", line 67, in changed_files
worker_8 |     .splitlines()))
worker_8 | TypeError: sequence item 0: expected str instance, bytes found
worker_8 |
worker_8 | During handling of the above exception, another exception occurred:
worker_8 |
worker_8 | Traceback (most recent call last):
worker_8 |   File "/tmp/python_workspace-command-flake8_diff-43ff8293/env/bin/flake8-diff", line 9, in <module>
worker_8 |     load_entry_point('flake8-diff==0.1.1', 'console_scripts', 'flake8-diff')()
worker_8 |   File "/tmp/python_workspace-command-flake8_diff-43ff8293/env/lib/python3.4/site-packages/flake8diff/main.py", line 132, in main
worker_8 |     parser.error(e.message or six.text_type(e))
worker_8 | AttributeError: 'TypeError' object has no attribute 'message'

[gregarmer]

Thanks @mikewaters :+1:

Can you bump the version in flake8diff/__init__.py so I can push a new version up to pypi.

[gregarmer]

Actually, nevermind - I want to turn on more py3k version tests in TravisCI, so I'll bump it once I've done that.

[mikewaters]

Sorry @gregarmer , just saw this. Thanks for the push.