Extended system_com and system_com_vel to properly work with particles of different masses. Old implementation is used if MASS is disabled.
Also added documentation for those two and galileiTransformParticles and deleted the respective todo notes.
Changed 'galileiTansformParticles' so that it gives a proper result n…
…o matter whether MASS is switched on or off.
Added documentation for 'galileiTransformParticles', 'system_com' and…
Excellent! I have pulled thes commits even into the 3.1 branch.