Documenting that json.load may raise a ValueError.

Issue #18680: JSONDecoder should document that it raises a ValueError
  for malformed data
Increasing test coverage of ftplib. Patch by Muhammad Jehanzeb
Issue 18724: Fix typo noticed by Susan Tan.
#18687: remove obsolete comment.  Patch by F?vry Thibault.
Add NEWS entry for 0f17aed78168 (issue #16248)