Merge #17435: Don't use mutable default values in Timer.

Patch by Denver Coneybeare with some test modifications by me.

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

diff --cc Lib/threading.py
Simple merge

diff --cc Misc/NEWS
index 2af6102d996f4f6405e1b40b136f8c76ccfa4f0d,beb3a8df392c6ec685f2f930ac1d6eb15cc8ffba..b5ea6c8ba602255f5bb2f33ec673c12f4df60d11
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -297,16 -214,8 +297,19 @@@ Core and Builtin
  Library
  -------
  
++- Issue #17435: threading.Timer's __init__ method no longer uses mutable
++  default values for the args and kwargs parameters.
++
 +- Issue #17526: fix an IndexError raised while passing code without filename to
 +  inspect.findsource().  Initial patch by Tyler Doyle.
 +
  - Issue #17540: Added style to formatter configuration by dict.
  
 +- Issue #16692: The ssl module now supports TLS 1.1 and TLS 1.2.  Initial
 +  patch by Michele Orrù.
 +
 +- Issue #17025: multiprocessing: Reduce Queue and SimpleQueue contention.
 +
  - Issue #17536: Add to webbrowser's browser list: www-browser, x-www-browser,
    iceweasel, iceape.