Merge branch 'jx/branch-vv-always-compare-with-upstream'

"git branch -v -v" (and "git status") did not distinguish among a
branch that does not build on any other branch, a branch that is in
sync with the branch it builds on, and a branch that is configured
to build on some other branch that no longer exists.

* jx/branch-vv-always-compare-with-upstream:
status: always show tracking branch even no change
branch: report invalid tracking branch as gone

diff --cc builtin/branch.c
Simple merge

diff --cc remote.c
Simple merge

diff --cc wt-status.c
Simple merge