Msg) firing a 2nd draw() before the fir(st has finished... This is a
general problem with our "pseudo-threaded" (i.e. putting many
WID->check() calls) approach... I added a new lock in draw() (we
already have one in Generate()), but this is pretty ugly.

"save as" stuff. This will only work with fltk > 1.1.0rc4 (Michael
Sweet added 2 functions to the fltk file chooser specially for us!)