[issue20851] Update devguide to cover testing from a tarball

[Brett Cannon]

New submission from Brett Cannon:

Nick Coghlan brought up the fact that with Larry Hastings doing periodic tarball dumps for the 3.4.0 release it would be good to make sure instructions on how to actually test from a tarball were in the devguide.

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components: Devguide
messages: 212722
nosy: brett.cannon, ezio.melotti
priority: normal
severity: normal
status: open
title: Update devguide to cover testing from a tarball
versions: Python 3.4

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue20851>
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