Dist fixes

This PR includes two commits. The first is a fix for a bug. When using the distutils upload command, the upload would fail with this error:

```
running upload
Traceback (most recent call last):
  File "C:\Users\jaraco\projects\workalendar\setup.py", line 57, in <module>
    'Programming Language :: Python :: 3.3',
  File "c:\python\lib\distutils\core.py", line 149, in setup
    dist.run_commands()
  File "c:\python\lib\distutils\dist.py", line 955, in run_commands
    self.run_command(cmd)
  File "c:\python\lib\distutils\dist.py", line 974, in run_command
    cmd_obj.run()
  File "c:\python\lib\distutils\command\upload.py", line 65, in run
    self.upload_file(command, pyversion, filename)
  File "c:\python\lib\distutils\command\upload.py", line 163, in upload_file
    body.write(value)
TypeError: 'str' does not support the buffer interface
```

It turns out that distutils is very particular about the types of the 'classifiers' (or any other value passed as metadata). If it's a tuple, it assumes it's a two-tuple of file/content. Because 'classifiers' was a tuple, the first two values were being loaded as file/content and the rest discarded, but since the second classifier was a string and not bytes, it was failing the upload. Making classifiers a list fixes this problem.

The second change is more stylistic, but it's a pattern which I've adopted and treats me well.

Feel free to accept the PR as-is, pull only the first commit, or ask me to update the PR to exclude the second change.