check-ref-format doc: --branch validates and expands <branch>
"git check-ref-format --branch $name" feature was originally
introduced (and was advertised) as a way for scripts to take any
end-user supplied string (like "master", "@{-1}" etc.) and see if it
is usable when Git expects to see a branch name, and also obtain the
concrete branch name that the at-mark magic expands to.
Emphasize that "see if it is usable" role in the description and
clarify that the @{...} expansion only occurs when run from within a
repository.
[jn: split out from a larger patch]
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>