Fix issue #6973: When we know a subprocess.Popen process has died, do

not allow the send_signal(), terminate(), or kill() methods to do
anything as they could potentially signal a different process.

diff --cc Misc/NEWS
index 16e79992097e7108622eb589f775393d0e586765,41ed26213bc045689cc16f87b4d04181a653ec8d..29843775962c445b0caac77018e7204fe351020c
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -88,14 -70,12 +88,18 @@@ Core and Builtin
  Library
  -------
  
+ - Issue #6973: When we know a subprocess.Popen process has died, do
+   not allow the send_signal(), terminate(), or kill() methods to do
+   anything as they could potentially signal a different process.
+ 
 +- Issue #23883: Added missing APIs to __all__ to match the documented APIs
 +  for the following modules: csv, enum, ftplib, logging, optparse, threading
 +  and wave.  Also added a test.support.check__all__() helper.  Patches by
 +  Jacek Kołodziej.
 +
  - Issue #25590: In the Readline completer, only call getattr() once per
 -  attribute.
 +  attribute.  Also complete names of attributes such as properties and slots
 +  which are listed by dir() but not yet created on an instance.
  
  - Issue #25498: Fix a crash when garbage-collecting ctypes objects created
    by wrapping a memoryview.  This was a regression made in 3.5a1.  Based