Merge branch 'mg/detached-head-report'

"git branch" on a detached HEAD always said "(detached from xyz)",
even when "git status" would report "detached at xyz".  The HEAD is
actually at xyz and haven't been moved since it was detached in
such a case, but the user cannot read what the current value of
HEAD is when "detached from" is used.

* mg/detached-head-report:
branch: name detached HEAD analogous to status
wt-status: refactor detached HEAD analysis

diff --cc builtin/branch.c
Simple merge

diff --cc wt-status.c
Simple merge