Read NumPart_Total and NumPart_Total_HighWord as unsigned ints
Read NumPart_Total and NumPart_Total_HighWord as unsigned ints

In Eagle, Illustris and Gadget HDF5 snapshots these attributes are
unsigned ints. Reading them into signed ints would cause the particle
number to be read incorrectly when either attribute has values
in the range 2**31 to 2**32-1 (e.g Eagle 100Mpc boxes).

pelahi/VELOCIraptor-STF,pelahi/VELOCIraptor-STF,pelahi/VELOCIraptor-STF