Merge branch 'NIFTy_7' into metric_tests
Fixed Fisher tests. The following bugs were present: - Metric of VariableCovarianceGaussianEnergy was wrong (already fixed in NIFTy+7, was fixed by merging) - debugging factor was not used, thus leading a false 'did not raise' assertion - the fast Fisher test for the VariableCovarianceGaussianEnergy was totally broken - slightly decreasing the tolerance for the isher test leads to factors of 2 being detected