Add a separate timer for subset sub-cell tasks. Write the timers to a file. Make sure we can compile without timers. Add a configure option to switch the timers on.

Don't lock the tree for the grav_init task. Don't call the unsorted pairs at all. Skip the entire zeroing loop when no xparts in runner_do_sort()

sort and drift on-demand in a consistent way. yes, even for the force loops as changes in the smoothing lengths may require a re-sort or interactions at a different level.

Created a function that branches calls to DOPAIR1 so that correct version is called. This decision is based upon whether MPI is running, vectorisation and orientation of the neighbouring cells.

Call runner_doself1_density_vec in DOSUB_SELF1 if vectorisation is enabled. Changed all WITH_VECTORIZATION macros to WITH_OLD_VECTORIZATION.

one big messy commit for the status quo, forces sorts of the active cells in each step, does not use task_type_sub_*, and probably sorts some cells twice. but it works.

Check that the particles interacting in the SELF or PAIR tasks have been properly drifted to the current time