[Polyworld-develop] don't put Polyworld in the background on Macs

[Larry Y. <la...@in...>]

A hard-won lesson:  Do not put Polyworld into the background while it 
is running, ever, if you care about the results, at least on 
Macintoshes.

All but the main overview window, including the agents' POV window, 
are "tool" windows.  When an app stops being frontmost, tool windows 
are automatically hidden.  That means the agent POV rendering and 
subsequent pixel reading to produce their vision inputs are being 
done to a hidden window, which does not produce valid results, at 
least under some conditions on some machines.

I've confirmed that making the POV window a normal (as opposed to 
tool) window eliminates the problem, but it raises other UI issues I 
don't want to solve right now.  If there's a way to not hide tool 
windows, that might be the easiest fix.  But the best fix would be to 
make the POV rendering work correctly whether the POV window is 
hidden or not.  Someday...

This probably does not affect Linux boxes, because I don't think 
Linux auto-hides tool windows.  Or perhaps rendering to hidden 
windows is no different than rendering to visible windows on Linux. 
In any event, putting Polyworld into the background on at least one 
Linux box did not affect the simulation.

The simulation is also unaffected by manipulating (closing, opening, 
moving) other windows in Polyworld, including on a Mac, even if they 
overlap the POV window.  Just don't close the POV window.

- larryy