merge 3.5

Issue #26804: urllib.request will prefer lower_case proxy environment variables
over UPPER_CASE or Mixed_Case ones.

Patch contributed by Hans-Peter Jansen. Reviewed by Martin Panter and Senthil Kumaran.

diff --cc Lib/urllib/request.py
Simple merge

diff --cc Misc/ACKS
Simple merge

diff --cc Misc/NEWS
Simple merge