async date loading

 * asynchronous date loading interleaves the loading by loading chunks and releasing control back to the browser every once in a while
 * when a date is loaded, let the ui first handle the redrawing events and only then notify the date was already loaded
Probably doesn't make much difference, and I'm not going to ask you to change it. I just noticed it because for loops where you don't have all three parts of the loop construct always make me think twice.