Testbranch - AI Humanity Change Cases

Initial attempt at adding different player humanity change cases into the on_kill function.  When using the spawn_group function, the 9th argument will be a string denoting "bandit" or "hero", which will tell the on_kill function whether to add or subtract humanity from the player when the unti has been killed.  Using the case structure approach for the two alignments was done to allow for further alignments to be added in the cases of VIPs, Super AI, or hostages.  The spawn_group function should default the alignment to "bandit" if it is not set in the call of the function.  Currently, this call will only work with "mission" units due to the way the mission variable is set.

Also, this is untested on a live server, so please review before merging the changes.