cc: @gtribello

It looks like the change was implemented separately in 2.4 and 2.5

should be not important. In particular, when invsigma was <10-12
sigma was set as equal to invsigma. Now it is set to zero,
which I think is the expected behavior.

When conda build fails, the travis job should return an error.

@tonigi

I verified it, I will then modified a regtest so to keep checking for this