Issue #19912: Fixed numerous bugs in ntpath.splitunc().

* splitunc() no more returns illegal result for paths with redundant slashes.
* splitunc() now correctly processes the u'İ' character
  (U+0130, LATIN CAPITAL LETTER I WITH DOT ABOVE).
* Added new tests for splitunc().
diff --git a/Misc/NEWS b/Misc/NEWS
index 3c94814..44ec6f1 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -23,6 +23,8 @@
 Library
 -------
 
+- Issue #19912: Fixed numerous bugs in ntpath.splitunc().
+
 - Issue #19623: Fixed writing to unseekable files in the aifc module.
   Fixed writing 'ulaw' (lower case) compressed AIFC files.