JDK 9 RFC on 6667086: Double.doubleToLongBits(final double value) contains inefficient test for NaN

[Brian Burkhalter]

Issue:	https://bugs.openjdk.java.net/browse/JDK-6667086
Webrev:	http://cr.openjdk.java.net/~bpb/6667086/webrev/

According to micro-benckmarks, there is no statistically significant performance change due to applying this patch but the code definitely looks cleaner.

Thanks,

Brian