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ARROW-339: [Dev] Lingering Python 3 fixes

I missed a couple Python 3 things. I'll leave this open until one of us successfully merged another patch with this before we merge it.

Author: Wes McKinney <wes.mckinney@twosigma.com>

Closes #191 from wesm/ARROW-339-2 and squashes the following commits:

78bf094 [Wes McKinney] Lingering Python 3 fixes