Location of screenshot

[Rik]

1/13/17

I'm trying to resolve bug #49952 (xml appdata file is invalid) on the
stable branch.  There are several issues, but one is that the screenshot
URL is invalid.  I get a 404 error when I try
http://www.gnu.org/software/octave/images/screenshot.png.

It appears that the new screenshot is located at
http://www.gnu.org/software/octave/img/screenshot-octave-4-2.png.

Questions:

1) Is that the correct image to use?
2) Is there any problem moving to https for the URL?
3) For future-proofing, shouldn't this image be renamed to screenshot.png? 
Otherwise, we would probably want to update the appdata file at every
release and do a new screenshot for every release, which sounds like more
work than necessary.  If I'm right, could someone who maintains the website
change the file and HTML?

Cheers,
Rik