function logcdf( x, mu, sigma ) {
	var lx = ( x <= 0.0 ) ? NINF : ln( x );
	return nlogcdf( lx, mu, sigma );
}
Evaluates the natural logarithm of the cumulative distribution function (CDF) for a lognormal distribution with mean `mu` and standard deviation `sigma` at a value `x`.

@param {number} x - input value
@param {number} mu - mean
@param {NonNegativeNumber} sigma - standard deviation
@returns {number} logarithm of cumulative distribution function

@example
var y = logcdf( 2.0, 0.0, 1.0 );
// returns ~-0.2799

@example
var y = logcdf( 13.0, 4.0, 2.0 );
// returns ~-1.442

@example
var y = logcdf( NaN, 0.0, 1.0 );
// returns NaN

@example
var y = logcdf( 0.0, NaN, 1.0 );
// returns NaN

@example
var y = logcdf( 0.0, 0.0, NaN );
// returns NaN

@example
// Negative standard deviation:
var y = logcdf( 2.0, 0.0, -1.0 );
// returns NaN

@example
var y = logcdf( 2.0, 8.0, 0.0 );
// returns -Infinity

@example
var y = logcdf( 8.0, 8.0, 0.0 );
// returns -Infinity