<Swing Dev> RFR: 8016451 : scary messages from Nimbus PainterGenerator during JDK build

[Phil Race]

http://cr.openjdk.java.net/~prr/8016451/
https://bugs.openjdk.java.net/browse/JDK-8016451

This eliminates the 20 or so messages like this
[Error] encoded value was less than 0: encode(-8.326673E-17, 5.0, 11.0, 
16.0)

I know these messages  vex many people.
These messages seem to be warnings at best, not an error
as far as the build is concerned and appear liikely to come down
to introduced FP error. Given that they have always been there
for nimbus on all platforms and appear harmless, since the
code fixes up the result anyway,  the safest thing to do is suppress them.
If anyone later wants to take up the gauntlet of adjusting/fixing
the math they are welcome to do so ..

-phil.