Improve progress monitor for jobs

@devoncarew

Improves upon #2688:
* uses the progress monitor's title in the status message, not the job's name
* formats the progress value as "x%", "x of y", "x.y" instead of always "x.y"

Also fixes a checked mode exception and adds an assertion.
Should we put some default text here ?

Sometimes i have seen the status bar is shown with no text, and it looks odd.