Bugfix and cosmetic changs in impl/praticles_type.h
Bugfix and cosmetic changs in impl/praticles_type.h

- Qualify the constants for the default MemPool alignment and chunk size with
  _MEMPOOL_ in their names, so as to avoid collision with future constants for
  different memory pool allocations

- Fix a bug in NS(Particles_assing_ptr_to_chi) where the wrong internal member
  (p0c) was used due to a copy&paste error

SixTrack/SixTrackLib,SixTrack/SixTrackLib,SixTrack/SixTrackLib,SixTrack/SixTrackLib