Only check that the cells at or below the super pointer have been drifted. No drift occurs above so checking is a bad idea.

When forming a star in a cell that never had a star before, set the ti_old_part to the current time.

Authorize the creation of new stars over MPI. Extra space is allocated at the end of the local cells only.

Lock the top-level cell in the star formation task to make sure we can safely re-arrange the particles in memory.

This reverts commit be1c1672.

This reverts commit 6ad75bd5.

Only set a common super-cell pointer if we are running with the policy corresponding the to the hydro/grav pointer we are looing for.

Added a force-communication with its dependency on the drift to make sure the data is correctly drifted before being received in the star loop.

Correctly activate all the send/recv and drifts of stars. Can now run EAGLE-6 over MPI with everything switched on.