OPTIONAL
SYNOPSIS
	int set_light(int n)

DESCRIPTION
	An object is by default dark. It can be set to not dark by
	calling set_light(1). The environment will then also get this
	light. The returned value is the total number of lights in
	this room. So if you call set_light(0) it will return the
	light level of the current object.
	
	Note that the value of the argument is added to the light of
	the current object.

BUGS
	This handling of light by the parser is inappropriate for most
	purposes: If you put a burning candle into a safe, the safe
	will start to emit light.
