Merge pathlib fixes

diff --cc Lib/pathlib.py
Simple merge

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

diff --cc Misc/NEWS
index edd46d86cb05ad2e9eacbcb4a7d7b2cd9e64c4ad,37d16eb5cfeada63012adf30a7f695668b1ae9d7..ca703fb0bef2b28783b28c819dbeb5504dee8518
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -108,8 -27,14 +108,14 @@@ Core and Builtin
  Library
  -------
  
 -- Issue #21897: Fix a crash with the f_locals attribute with closure
 -  variables when frame.clear() has been called.
+ - Issue #20639: calling Path.with_suffix('') allows removing the suffix
+   again.  Patch by July Tikhonov.
+ 
+ - Issue #21714: Disallow the construction of invalid paths using
+   Path.with_name().  Original patch by Antony Lee.
+ 
 +- Issue #15014: Added 'auth' method to smtplib to make implementing auth
 +  mechanisms simpler, and used it internally in the login method.
  
  - Issue #21151: Fixed a segfault in the winreg module when ``None`` is passed
    as a ``REG_BINARY`` value to SetValueEx.  Patch by John Ehresman.