avoid boxing

[xuwei-k]

scala.runtime.Rich{Double, Float} has isNaN and these are value class.
Also java.lang.{Double, Float} has isNaN.

• https://docs.oracle.com/javase/8/docs/api/java/lang/Double.html#isNaN--
• https://docs.oracle.com/javase/8/docs/api/java/lang/Float.html#isNaN--

We can't call RichDouble#isNaN because
implicit def double2Double(x: Double): java.lang.Double
is higher priority than
implicit def doubleWrapper(x: Double): RichDouble

$ scala -version
Scala code runner version 2.11.8 -- Copyright 2002-2016, LAMP/EPFL

$ scala -Xprint:jvm -e "1.0.isNaN"
[[syntax trees at end of                       jvm]] // scalacmd616162202928036892.scala
package <empty> {
  object Main extends Object {
    def main(args: Array[String]): Unit = {
      new <$anon: Object>();
      ()
    };
    def <init>(): Main.type = {
      Main.super.<init>();
      ()
    }
  };
  final class anon$1 extends Object {
    def <init>(): <$anon: Object> = {
      anon$1.super.<init>();
      scala.this.Predef.double2Double(1.0).isNaN();
      ()
    }
  }
}

[retronym]

This implicit situation here is pretty unfortunate. Would be nice to train -opt to deal with this, but for now your patch looks like a pragmatic solution.

LGTM