Log Message:
py-subprocess32: update to 3.5.2.

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2018-06-07 3.5.2
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* Explicitly include <signal.h> in _posixsubprocess_helpers.c; it already
  gets configure checked and pulled in via Python's own <Python.h> in many
  circumstances but it is better to be explicit.  #IWYU
  If you were using subprocess32 on a Python interpreter built *without*
  the --with-fpectl configure option enabled, restore_signals is now
  useful rather than a no-op.  I do not know if such builds were common.
* Adds a functional test for restore_signals=True behavior.