Merge branch 'hn/status-compare-with-push' into seen

"git status" learned to show comparison between the current branch
and its push destination as well as its upstream, when the two are
different (i.e., triangular workflow).

Comments?

* hn/status-compare-with-push:
  status: show comparison with push remote tracking branch
  refactor format_branch_comparison in preparation

diff --cc remote.c
Simple merge