when adding a new obejct class:

In defs.h:
	add its OC_ enum 

In objects.c:
	define the class with addoc()
	add the class to sortorder[] at the top
	findotn() must know how to un-pluralise the name (eg. potions)

	update genhiddenname() if this class isn't known
		also add hidden names up the top
		also update numXXXnames count in initobjects()

In text.c:
	makeplural() must know about the name (eg. potion -> potions)