Make the bots drop broken bot items instead of corpses [CR]

Changed the mondeath::broken function to create a broken_xxx item where xxx is the monster id minus the mon_prefix. That death function has been added to the other bots instead of the normal death function.

This prevents the bots from dropping corpses.

I also added the items that are created there. They have the same values as the broken manhack, because they are actually copies of it. The items are currently useless as they have no disassemble recipe. Sadly I have no creativity for this.

Or should the butchering be changed so that butchering a tankbot "corpse" is actually disassembling the tank bot "corpse"?

The tribot has id mon_tripod?