Split file in case of more than 5000 nodes, and the OsmChange format is slightly different.
Increase precision of coordinates.
Change reader to read the new format.
Correct starting XML tag for OsmChange and the file filter in the save dialog.
Change file name generation to allow for any extension, and so that the extension can be specified in the text box.
Disable the convert button until processing is finished, so that the user knows he/she clicked it.
Create a cleanup() method that clears (nearly) everything and gets called at the end and two failure points.