Fit result display gets garbled if fit is run more than once

[ajj]

The red text in the Curve Fit Setup panel becomes garbled if you run a fit more than once - say you fit different parameters or switch to a different model.

It clears up if you switch models or datasets.

[srkline]

This appears to be only a problem on windows, and will require some testing to find a common solution

[srkline]

the garbling seems to be a windows redisplay issue when the panel is partially covered by say, an OS dialog. Not much I can do about that. the other issue of the ugly GroupBox? lines appearing on Windows and not on Mac may just be a fluke on the Mac. The lines probably should be there. As a suitable workaround, I've set the size to {0,0}, leaving little more than smudges. Good enough.