Progress on 2.2a

Release 2.2a is very nearly ready (barring some catastrophe). Aside from a few 'nice-to-haves', 2.2a will add a 'cancel' button to most progress dialogs. To do this, I've had to create a worker thread to run the calculations, thereby freeing-up the main application thread so that it may respond to windows messages (ie 'cancel').

It all seems to work OK, but I want to spend a bit more time on the validation and debugging stage, as poorly threaded applications are really bad news.