This is a relic of a long-gone past where marktasks and unskip needed to be different. Now it just makes use duplicate entire code blocks for no good reasons.
engine_unskip() is superior as it only loops over the tree sections where actual work could happen, so that's the version we should keep.
This version keeps marktasks as a way to verify unskip's job. Once we are happy they are identical (as they should) we can remove that check.
Actual changes to keep past these tests:
- Better names for the various BH ghosts between the task names and the cell-carried task pointers.
- More uniform activation (for readability) of the gravity drift related to MPI between unskip and marktasks.
- Fix a mismatch where marktasks was activating unnecessary star pairs.
- Fix a mismatch where marktasks was activating unnecessary BH ghosts.
- Fix a mismatch where markatask was not activating star drifts in the case of stars doing only gravity.
- Fix a mismatch where marktasks was not activating RT_in tasks.