Add some UNLEAKs where we are about to return from `cmd_*`. UNLEAK the
variables in the same order as we've declared them. While addressing
`msg` in builtin/tag.c, convert the existing `strbuf_release()` calls as
well.
Signed-off-by: Martin Ågren <martin.agren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>