stupid multifractality

also, fix max_estimate value in call to vorticity moments

first of all, moments were completely broken because fields weren't
prepared properly.
secondly, normalization is not actually required.

at the moment it's broken because I needed to change the prototype of
rspace_stats.

first of all, the struct being used was wrong before, it had double
instead of C_dtype.
secondly, the dtype should be closed before the fluid solver is
deallocated, since I use a check after fs->cd->myrank == 0.

HDF5 is complaining that I'm closing an invalid dtype, no idea what
that's about...

I think. still checking...