Fix an issue with Python 3

The code in ftplib checks port > 0. This works with port = None in Python 2
because it allows such comparisons, but Python 3 is more strict. The solution
(I think) is to just use the default port, 0, in this case.
Merge pull request #2 from asmeurer/python3

Fix an issue with Python 3
Add GET as an alias for retr
Login before trying to download
Address comments from the pull request

- It is not necessary to monkeypatch get
- The login call should be in send, not retr
Merge pull request #4 from asmeurer/get

Fixes #3
Mention @asmeurer in AUTHORS.
V0.2.0
Fix url in setup.py
Merge pull request #5 from reclosedev/patch-1

Fix url in setup.py
Merge pull request #1 from Lukasa/master

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