Issue #25523: Merge a-to-an corrections from 3.5

diff --cc Doc/library/multiprocessing.rst
Simple merge

diff --cc Doc/library/pickle.rst
Simple merge

diff --cc Lib/_pyio.py
Simple merge

diff --cc Lib/calendar.py
Simple merge

diff --cc Lib/pickle.py
Simple merge

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

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

diff --cc Lib/tkinter/ttk.py
Simple merge

diff --cc Misc/NEWS
Simple merge

diff --cc Modules/_collectionsmodule.c
Simple merge

diff --cc Modules/_io/_iomodule.c
Simple merge

diff --cc Modules/_pickle.c
Simple merge

diff --cc Modules/readline.c
Simple merge

diff --cc Python/compile.c
Simple merge