Change mentions of <object> to <commit> in the help output of
for-each-ref as appropriate.
Both --[no-]merged and --contains only take commits, but --points-at
can take any object, such as a tag pointing to a tree or blob.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>