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ARROW-3012: [Python] Fix setuptools_scm usage

We were using a deprecated / unofficial API together with hand-written version parsing.
We can just pass a custom git tag regex instead.

Also, harden the fallback in setup.py when we're not in a git clone (typically when running `pip install`, as pip always copies the project directory before acting on it).
Include a clear error message when not able to infer the Arrow version, to let people
know how to workaround the issue.

pip-installing source distributions should now work fine (and get the right version
number).

Author: Antoine Pitrou <antoine@python.org>

Closes #2413 from pitrou/ARROW-3012-fix-setuptools-scm-usage and squashes the following commits:

5369d640 <Antoine Pitrou> Re-add a parse function to avoid non-C++ tags
2a93f9cc <Antoine Pitrou> ARROW-3012:  Fix setuptools_scm usage