deduplicate contributors by e-mail

def get_contributors(git_dir):

    result = set()

    emails = set()

    for x in git(git_dir, "log", "--format=%aN").splitlines():

        if x != "root":

            result.add(x)

    for x in git(git_dir, "log", "--format=%aN|%aE").splitlines():

        name, email = x.rsplit("|", 1)

        if name != "root" and email not in emails:

            emails.add(email)

            result.add(name)

    return list(sorted(result, key=lambda x: x.lower()))