[issue15415] Add temp_dir() and change_cwd() to test.support

[Terry J. Reedy]

Terry J. Reedy added the comment:

As of this moment, the test has run on one of the two Win7 machines and the xp buildbot. It also runs by itself on my win7 desktop with a fresh pull.

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue15415>
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