applies same tweaks that were needed for the spherical ghost collision
counter.

for some reason it only works like this on one machine

cmake config can no toggle the use of "NDEBUG" or "USE_TIMINGOUTPUT"
compiler flags, hence source files and/or .bashrc no longer need to be changed
themselves.
I'm not sure the mechanism survives very nicely for executable
compilation, but it's better to have it and figure that out later.

checkpoint is somewhat improper because checkpointing functionality was
implemented in vorticity_equation instead of
direct_numerical_simulation, so that would be the next step.

preliminary test works with no obvious problems.

this is not nice at all, but the purpose is to have basic functionality
for testing. It's pretty obvious this will need a custom launcher for
production work.

now code compiles

change actually made by chichi on Tobias's computer.
blame him.

launcher checks that stored iteration and checkpoint in <simname>.h5 are
consistent, i.e. <simname>_checkpoint_<checkpoint_value>.h5 contains
field at iteration.
useful when DNS are restarted for various reasons.

also corrects `joint_acc_vel_stats`, in the sense that forcing
parameters should be read beforehand if the acceleration statistics are
to make sense.