I made some of the unit tests less tight. They were based on noise levels from the original version of stats.sigma_clip, with very little margin, as if the original stats.sigma_clip was perfect. This original version, however, failed for images with a very high source density. The present version gives slightly lower noise levels in these circumstances and closer to the ground truth.
I made some of the unit tests less tight. They were based on noise levels from the original version of stats.sigma_clip, with very little margin, as if the original stats.sigma_clip was perfect. This original version, however, failed for images with a very high source density. The present version gives slightly lower noise levels in these circumstances and closer to the ground truth.

transientskp/pyse,transientskp/pyse