Add new function to decide on recursion with in a sub_pair task. Makes sure all recursion tests are identical.

change sort task flags to be zero by default and only switch on those that are needed, avoids pre-emptively computing all the sorts for a cell since they may never be needed between two sort cleanups.

activate sorts and drifts in sub-cell tasks explicitly, store current values for h_max, dx_max, and dx_max_sort for consistency.

Removed the 'tight' property of the tasks. Only density pairs need to be tight so we can just use that.