status: count push divergence outside the upstream - #2437

After rebasing onto a newer upstream, "git status" counts every commit
the upstream gained since the last push as a difference from the push
branch when status.compareBranches includes "@{push}". That can be many
commits, even when only a few of your own differ.

Keep the full counts, and when they include commits from the upstream,
add how many of them are not in it:

  Your branch and 'origin/topic' have diverged,
  and have 51 and 1 different commits each (1 and 1 not in 'upstream/main').

When the commits outside the upstream carry the same changes on both
sides, say so:

  Your branch and 'origin/topic' have diverged,
  and have 51 and 1 different commits each (rebased cleanly on 'upstream/main').

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>