architecture-dependent results for GaussianDistribution example

Issue #1041 (closed) showed problems with cross-platform deployment, see https://buildd.debian.org/status/package.php?p=bornagain.

Most notably, the persistence test for case 2 (of cases 0,1,2,3) of the GaussianDistribution shows grossly different numerical values of I(alpha) for the smallest values of alpha. For the very first value of alpha, 0.87 vs 0.81.