function isPrime( x ) {
	return Boolean( addon( x ) );
}
Tests if a finite double-precision floating-point number is a prime number.

@private
@param {number} x - value to test
@returns {boolean} boolean indicating whether the number is prime

@example
var bool = isPrime( 2.0 );
// returns true

@example
var bool = isPrime( -5.2 );
// returns false