// General 'load and run code from server' function with callback parameter
// Code adapted from example in PHP Architect
function loadCodeFromServer(scriptname, params, callback) {
  var head = document.getElementsByTagName('head').item(0);
  var oldhead = document.getElementById('loadedScript');
  if (oldhead) {
    head.removeChild(oldhead);
  }
  var script = document.createElement('script');
  script.src = scriptname + (callback ? '?callback='+callback+(params ? '&'+params : '') : (params ? '?'+params : ''));
  script.type = 'text/javascript';
  script.defer = true;
  script.id = 'loadedScript';
  head.appendChild(script);
}