Lfun:	add_weight - add weight to an object

Synopsis:
	int add_weight(int weight)

Description:
	Any object that can contain other objects must define this function.
	It is called with the extra weight of the new object. This function is
	called automatically from the transfer efun.

Return value:
	If this is ok, it has to increment the local weight count and return 1.
	Otherwise it has to return 0 and the new object cannot enter it

Examples: see the obj/container.c code

See also: object/query_weight, efun/transfer