keep reverse sorted mapped indexes in addition to forward

buffer_reversestring.js

function reverseString(sin) {
    sin = new Buffer(sin);
    for (var idx = 0, l = sin.length; idx < l; idx++) {
        sin.writeUInt8(0xFF - sin.readUInt8(idx), idx);
    }
    return sin;
}

riak_reverse_put.js

function reverseString(sin) {
    sin = String(sin);
    var out = '';
    for (var idx = 0, l = sin.length; idx < l; idx++) {
        out += String.fromCharCode(~ sin[idx].charCodeAt() & 0xFF);
    }
    return out;
}

function put(riak, opts, callback) {
    var indexes = opts.indexes || {};
    Object.keys(indexes).forEach(function (index) {
       if (Array.isArray(indexes[index])) {
           indexes['_reverse_' + index] = indexes[index].map(reverseString);
       } else {
            indexes['_reverse_' + index] = reverseString(indexes[index]);
       }
    });
    indexes['_reverse_$key'] = reverseString(opts.key)
    opts.indexes = indexes;
    riak.put(opts, callback);
}

function getByIndex(riak, opts, callback) {
    if (opts.reverse) {
        opts.index = '_reverse_' + opts.index;
        opts.key = reverseString(opts.key);
    }
    riak.getByIndex(opts, callback);
}