Account for bytes in Python 3

[neilmb]

This accounts (somewhat) for the difference between bytes and strings in Python 3. It fixes #38 in particular.

It also adds python 3 to the Vagrant VM for developers and defines a make test3 target for running the tests specifically under that python 3.

[b4hand]

I think instead of this you should change the mode for download_file to wb so that the file object will be in binary mode as well.

[neilmb]

I wish that was the fix. The test failure that needed fixing was on https://github.com/seomoz/s3po/blob/master/test/test_connection.py#L29 where it checks the result of self.conn.download. For the memory backend, download() grabs the actual python object that is stored, so when upload_file runs with mode rb, the value that the memory backend stores is bytes.

https://github.com/seomoz/s3po/blob/master/s3po/backends/memory.py#L20 is trying to write those bytes to into fobj which is a StringIO from https://github.com/seomoz/s3po/blob/master/s3po/connection.py#L79.

I'm totally not sure what the "right way" to handle the memory backend is in the face of string vs. bytes.

[b4hand]

It looks like the default for StringIO is to use the system locale via this method:

locale.getpreferredencoding(False)

I think that's preferable to specifying ascii since that could throw away bytes greater than 0x7f.