/*
convert a simple timespan string, expressed in days, hours, minutes, or
seconds, such as 30d, 12d, 8h, 45m, 30s, into a numeric quantity in
seconds.
function resolveExpiry(subject) {
    var pattern = new RegExp('^([1-9][0-9]*)([smhdw])$','i');
    var multipliers = {s: 1, m: 60, h : 60*60, d:60*60*24, w: 60*60*24*7, y: 60*60*24*365};
    var match = pattern.exec(subject);
    if (match) {
      return match[1] * multipliers[match[2]] * 1000;
    }
    return -1;
  }