function eliminar_opciones_cbo(combo){
		largo_cbo = combo.length;
		for (i=largo_cbo;i>=0;i--){
			combo.options[i]=null;
		}
	}
	
	function eliminar_opciones(combo){
		largo_cbo = combo.length;
		for (i=largo_cbo;i>=0;i--){
			combo.options[i]=null;
		}
	}

	function marcar_todos_cbo(combo){
		for (i=0;i<combo.length;i++){
			combo.options[i].selected = true;
		}
	}

	function marcar_selecciones_al_enviar(cbo1, cbo2){
		marcar_todos_cbo(cbo1);
		marcar_todos_cbo(cbo2);
		return true;
	}
	function marcar_seleccion_al_enviar(cbo1){
		marcar_todos_cbo(cbo1);
		return true;
	}
	
	function sortSelect(obj){
	    var o = new Array();
	    for (var i=0; i<obj.options.length; i++){
	        o[o.length] = new Option(obj.options[i].text, obj.options[i].value, obj.options[i].defaultSelected, obj.options[i].selected);
	    }
	    o = o.sort(
	        function(a,b){ 
	            if ((a.text+"") < (b.text+"")) { return -1; }
	            if ((a.text+"") > (b.text+"")) { return 1; }
	            return 0;
	        } 
	    );

	    for (var i=0; i<o.length; i++){
	        obj.options[i] = new Option(o[i].text, o[i].value, o[i].defaultSelected, o[i].selected);
	    }
	}