Correction of values instead of simple filtering.

Allows to account for situations where e.g. cases are big enough,
but controls are all below cutoff, yet there's a sizeable gap
between the groups (1/2 cutoff value).
Then those that are below are driven into zeros, and those that are
above are left as they are, allowing them to pass the filter that
is now called divergent().
Correction of values instead of simple filtering.

Allows to account for situations where e.g. cases are big enough,
but controls are all below cutoff, yet there's a sizeable gap
between the groups (1/2 cutoff value).
Then those that are below are driven into zeros, and those that are
above are left as they are, allowing them to pass the filter that
is now called divergent().