function isNegativeFinite( x ) {
	return Boolean( addon( x ) );
}
Tests if a double-precision floating-point numeric value is a negative finite number.

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

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

@example
var bool = isNegativeFinite( 5.0 );
// returns false