See the previous commit.  This is a bit of a doozy...the enemies now work
exactly as they did before I messed everything up!  The problem turned out
to be that things were getting created in the wrong order, so the enemy_defs
were trying to call EquipType items which didn't exist yet.  To fix it, I
combined all of the definitions into one file so I could control what order
they get created in.  Whew.  It is very possible for the enemies to be created
with a list of possible items, and they now do it in the defs file instead of
in a mess of subclass files.  And there's now only one enemies file.  I may move
the ai into an ai.h, although it's really  nice to have access to the enemy variables.