Use the list of sources instead of an iterator in update-feeds looping task
This prevents RuntimeError due to dictionary size change that may occur (as a
result of a new source being added) during iteration.
Closes #3155843.
[debian] add some Breaks for backwards compatibility removal
The person and comment cubes used to import the cubicweb.mixins module.
The inlinedit cube relied on String.startsWith in javascript.