This reverts merge request !375

Threadpool task plots

Adds the following:

 * `--enable-threadpool-debugging` to the `./configure` flags,
 * `-Y` to `main.c` to enable dumping threadpool timers much like the task timers.

This generates `threadpool_info-step%d.dat` files every `-Y` steps which contain the mapper function name, the id of the thread that executed it, the number of chunks processed, and the `tic` and `toc` timers for the mapper function.

See merge request !375

Fix to make test27cells still give 48 neighbours

Small change as test27fix we want to still output the weighted number of neighbours as described by other people.

See merge request !381

Random fixes

We only need `ti_sort` in debug mode.

See merge request !374

Merge branch 'threadpool_task_plots' of gitlab.cosma.dur.ac.uk:swift/swiftsim into threadpool_task_plots

keep a separate log buffer per thread id. this avoids having to protect against concurrent access to the logs.

Merge branch 'threadpool_task_plots' of gitlab.cosma.dur.ac.uk:swift/swiftsim into threadpool_task_plots

Fewer mpi comms

Re-think when and how we activate communication tasks and pair tasks spanning local and foreign cells.

This should result in much fewer interaction tasks, send/recv pairs, and drifts.

See merge request !373

Make SWIFT static library a dependency of all tests

We need to rebuild those after any updates.

Fixes #329. 

See merge request !376