fix handledamage and forceprone

atm, handledamage change all damage part every hit so, you can Heal player with a hit ! 
I change damages calcul : i add new damage to current player damage and set new partdamage to player.
i also fix #684 (Prevent multiple damages replace selectionpart with another)

i add a "1 sec allowDamage" false on knockdown for prevent death with shotgun etc.

and finaly i fix "break legs" features with an eventhandlers animchange.

enjoy