Name: function_exists - check if a function exists in an object

Syntax:
	string function_exists(string str, object ob)

Description:
	The function_exists finds out if function str is defined in object ob.
	
Return value:
	If the function is not defined, 0 is returned. Else the file_name
	of the object that defines str is returned. This can be different
	from the filename of ob, if the function is defined by an inherited
	object.

Examples:
	string def;
	def=function_exists("init", this_object());

See also: efun/call_other