Merge branch 'js/pu-to-seen'

The documentation and some tests have been adjusted for the recent
renaming of "pu" branch to "seen".

* js/pu-to-seen:
  tests: reference `seen` wherever `pu` was referenced
  docs: adjust the technical overview for the rename `pu` -> `seen`
  docs: adjust for the recent rename of `pu` to `seen`

diff --cc Documentation/SubmittingPatches
Simple merge

diff --cc Documentation/howto/maintain-git.txt
Simple merge

diff --cc t/t5516-fetch-push.sh
Simple merge

diff --cc t/t9902-completion.sh
Simple merge