Clean code of pyflakes warnings

[adiroiban]

This is to fix #67

I have clean all code, excepting the functional test which are broken by design.

I have create a dedicated pyflakes runner which excepts functional tests.

Another option is to move those files outside of twistedchecker

I will try to send a patch upstream to pyflakes to allow excluding files as a similar exception is required for twisted.

Thanks!

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Can you put a commit on here so that travis will pick it up and tell us about build results?

[adiroiban]

I have updated the travis.yml to also run pyflakes for each commit....

I have also updated pip install to add the --upgrade flag. In this way pip will pin version specified in setup.py install_requires

in the future, I hope that we can run twistedchecker to check twistedchecker codebase...

[glyph]

Thanks for the update. Awesome!