function poisson2( lambda ) {
		if (
			isnan( lambda ) ||
			lambda <= 0.0
		) {
			return NaN;
		}
		return poisson0( rand, lambda );
	}
Returns a pseudorandom number drawn from a Poisson distribution.

@private
@param {PositiveNumber} lambda - mean
@returns {NonNegativeInteger} pseudorandom number

@example
var v = poisson2( 0.5 );
// returns <number>

@example
var v = poisson2( NaN );
// returns NaN

@example
var v = poisson2( -1.0 );
// returns NaN