function fallingFactorial( x, n ) {
	return addon( x, n );
}
Computes the falling factorial of `x` and `n`.

@private
@param {number} x - first function parameter
@param {NonNegativeInteger} n - second function parameter
@returns {number} function value

@example
var v = fallingFactorial( 0.9, 5 );
// returns ~0.644

@example
var v = fallingFactorial( -9.0, 3 );
// returns -990.0

@example
var v = fallingFactorial( 0.0, 2 );
// returns 0.0

@example
var v = fallingFactorial( 3.0, -2 );
// returns NaN