git-blame is slated to accept multiple -L ranges. git-log already
accepts multiple -L's but its implementation of range-set, which
organizes and normalizes -L ranges, is private. Publish the small
subset of range-set API which is needed for git-blame multiple -L
support.
Signed-off-by: Eric Sunshine <sunshine@sunshineco.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>