Made the check for unlock overflows active even when not running with debugging checks. Also updated the error message to give some guidance about what to do in these situations.

Rayleigh

See merge request !868

Fof io and compile without fof

See merge request !850

Short main.c cleanup

See merge request !870

Improve the logic in the BH sub-task recursion to make sure we also recurse if there is no gas in the cell as we need the recursion for the BH-BH merger detection.

Add eagle feedback test

See merge request !869

New random_unit_interval implementation

See merge request !866

Black holes mergers

See merge request !863

Fixes a bunch of warnings triggered by GCC 9.1

Closes #600

See merge request !867

replace the default random_unit_interval implementation with one that generates 48-bit mantissas using rand_r and erand48.

Fix diffusion velocity bug

See merge request !865

Added nIFTy cluster example

See merge request !864