Insert commodity object 'co' into the list of object connected to 'headObj' after the object 'pred'.
INPUTS
headObj
poiter to a list of objects to which 'co' shall be inserted
co
commodity object to be inserted (may be NULL)
pred
the object 'co' shall be inserted after (may be NULL)
RESULT
If 'headObj' is NULL, the object 'co' and all objects connected to it are deleted. If 'co' is NULL and 'headObj' is a valid object, the latter's accumulated error will be adjusted to incorporate COERR_NULLATTACH. If 'pred' is NULL, the object will be inserted first in the list.