As far as I can tell p_from_null was performing a specific function that was only used in the old isfc function, and is no longer referenced anywhere in brainiak. In this case, I think compute_p_from_null_distribution supersedes p_from_null, and p_from_null can be removed. However, I may shorten the name of compute_p_from_null_distribution as I only named it this to not overlap with the pre-existing p_from_null.
Replaced old p_from_null with newer functionality from compute_p_from_null_distribution in #405 (commit daa5d41). Note that the new functionality now uses the older simpler function name. This also required removing the ecdf functionality which is no longer used anywhere in BrainIAK (commit aa0c37d.