[code-quality] Small pyflakes surprise

[Skip Montanaro]

> Running "make lint" today, I saw pyflakes emit messages for a file
> named utils.py.~1~, that is, an Emacs backup file. This is a new file
> in my sandbox which hasn't yet been added to the Git repo, so Emacs
> knows to create backups. (Once checked in, it will rely on Git.) It
> seems odd to me that pyflakes would decide to check such a file. Is
> this a bug or a feature? Looks like we are running 1.6.0, which
> appears to be more-or-less current.

Issue and PR created:

https://github.com/PyCQA/pyflakes/issues/332
https://github.com/PyCQA/pyflakes/pull/331

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