This filters the list for tags of the given object.
Example,
john$ git tag v1.0-john v1.0
john$ git tag -l --points-at v1.0
v1.0-john
v1.0
Signed-off-by: Tom Grennan <tmgrennan@gmail.com>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>