function checkboxlist(stringname,checkboxvalue){
	if(document.getElementById(stringname).value.indexOf(","+checkboxvalue+",")!=-1){
		var regexp = eval("/,"+checkboxvalue+",/");
		document.getElementById(stringname).value = document.getElementById(stringname).value.replace(regexp,",");
	}else{
		document.getElementById(stringname).value += checkboxvalue + ","
	}
}