Issue #18418: After fork(), reinit all threads states, not only active ones.

Patch by A. Jesse Jiryu Davis.

diff --cc Lib/test/test_threading.py
Simple merge

diff --cc Lib/threading.py
Simple merge

diff --cc Misc/ACKS
Simple merge

diff --cc Misc/NEWS
index 0d7ba2fc3188036f374b1559cd9262b00359373d,d859de108012d0ed5bc84734e82fb5d4398c9523..dfba2cac0c93453e6de6c8d843914efb4d7648f9
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -51,10 -66,9 +51,13 @@@ Core and Builtin
  Library
  -------
  
+ - Issue #18418: After fork(), reinit all threads states, not only active ones.
+   Patch by A. Jesse Jiryu Davis.
+ 
 +- Issue #17974: Switch unittest from using getopt to using argparse.
 +
 +- Issue #11798: TestSuite now drops references to own tests after execution.
 +
  - Issue #16611: http.cookie now correctly parses the 'secure' and 'httponly'
    cookie flags.