lib/dRanNormalTail.js
function dRanNormalTail( dMin, iNegative, rand ) {
	var x, y;
	do {
		x = ln( rand() ) / dMin;
		y = ln( rand() );
	} while ( -2 * y < x * x );
	return iNegative ? x - dMin : dMin - x;
}
function dRanNormalTail( dMin, iNegative, rand ) {
	var x, y;
	do {
		x = ln( rand() ) / dMin;
		y = ln( rand() );
	} while ( -2 * y < x * x );
	return iNegative ? x - dMin : dMin - x;
}
NORMAL TAIL // 
FUNCTION dRanNormalTail( dMin, iNegative, rand )
Transform the tail of the normal distribution to
the unit interval and then use rejection technique
to generate standar normal variable.
Reference:
Marsaclia, G. (1964). Generating a Variable from the Tail
of the Normal Distribution. Technometrics, 6(1),
101–102. doi:10.1080/00401706.1964.10490150

@param {Number} dMin - start value of the right tail
@param {Boolean} iNegative - boolean indicating which side to evaluate
@param {Function} rand - random number generator
@returns {Number} standard normal variable