Checked if FastKdTree is really only 8 bytes. Found out that it's in
real 16 byte, but that's because my System is 64bit and pointer have 8
byte. So when FastKdTree has a FastKdTree* and a hpreal then it's in sum
12 byte. But the system seems to fill the bytes up to 16.

Janet or Simon has to check this on their systems, too.