Fix public repository listFiles method that I broke with PR669.

[mtbc]

In #669 I broke PublicRepositoryI.listFiles. This attempts to fix it. Using the command-line interface to try getting a repository and listing the files would be a good test. @joshmoore will have some thoughts on testing too.

[joshmoore]

Windows is certainly looking good:

In [3]: m.proxies[1].list(".")
Out[3]: ['/root_0']

In [4]: m.proxies[1].list("/")
Out[4]: ['/root_0']

I'll test more with my repository.py changes in just a bit.

[joshmoore]

My repository.py is now completely passing locally. I'll open a PR with it shortly, but this can certainly be assumed to be working. Thanks, Mark.