* progress bar now reflects actual completion of process more closely
* dropped the use of UM_FORMAT_PROGRESS and introduced UpdateProgress() instead
* also reduced the number of rw test patterns from 4 to 2
* after a bb check, MBR could become garbage
* when that occurs, Windows might interpret a bad partition table and prevent MBR from being properly written
* force a complete zeroing of the whole MBR before partitioning to fix this
* also added error code for bb