Lfun:	forbid_advance - forbid a player to advance

Synopsis:
	int forbid_advance()

Description:
	Define this function in an object that players can carry,
	if you want to prevent a player from advancing in a guild.

	This feature can be used to implement loans.

Return value:
	If the return value is 0, the player may advance, anything else means,
	that player is not allowed to advance. In this case the function
	should inform the player, why he can not advance and what he should do.

Examples:
	forbid_advance() {
		write("You still owe the bank of Nemesis money!\n");
		return 1;
	}