branch: name detached HEAD analogous to status

branch: name detached HEAD analogous to status

"git status" carefully names a detached HEAD "at" resp. "from" a rev or
ref depending on whether the detached HEAD has moved since. "git branch"
always uses "from", which can be confusing, because a status-aware user
would interpret this as moved detached HEAD.

Make "git branch" use the same logic and wording.

Signed-off-by: Michael J Gruber <redacted>
Signed-off-by: Junio C Hamano <redacted>