Add Bloax' sweet cacodemon tile to UNUSED/.

Here's a progress report about how doomed we are:

✓ various weapon-using zombies
✓ imp
    slightly hindered by 0.10-a0-1355-g43440df
✗ demon
    definable: a simple melee-only animal.  The name is too generic.
└ spectre (perm_ench:invis)
✓ lost soul
    flying skulls (more faithful) and lost souls (name).
✓ cacodemon
    spells are definable, inertia on being shot not.
✓ hell knight
└ baron of hell (exact rename with +hd)
✓ arachnotron
    orb spiders (could use a rapid-fire weapon)
✗ pain elemental
    definable: some eye spells:call_lost_soul
✓ revenant
    IOOD is a direct implementation of their weapon
✗ mancubus
✗ arch-vile
✗ spider mastermind
✗ cyberdemon
✓ some bastard that runs around and kills folks

Author: kilobyte