[updated] Mantis Bug #4204
Adjust aggro chance to take skill into effect. High skill vs CL less
likely to aggro. always a 5% chance to aggro on a success, unless the
creature can provide no more samples in which case it dies. Also added
some extra adjustments to ensure if you sample a creature to death you
may NOT harvest from the corpse. Also Fixed a missing mean * level in
the dna manager. for some reason have a line got cut off, recommiting

Change-Id: I916dd88a666afb89e9fe318a37c5b6c95ea12846