compiler was warning that something is reduced from int to hsize_t.

the "simname_particles.h5" file is now only opened once, and then
samples are written the same as before.
some sanity checks of the velocity and acceleration data should still be
performed.

Berenger Bramas authored 8 years ago and Cristian Lalescu committed 8 years ago

Add a sampling method -- update to be generic against the field -- need to update NSVEparticles::do_stats