function substituteFromURL(var_name,new_value){
	var found = false;
	var url = window.location.href;
	division = url.split("?");
	url = division[0] + "?";
	token = division[1].split("&");
	for(i=0;i<token.length;i++){
		if(token[i].substr(0,(var_name.length)) == var_name){
			//alert(token[i].substr(0,(var_name.length)));
			var_token = token[i].split("=");
			var_token[1] = new_value;
			token[i] = var_token[0] + "=" + var_token[1];
			found = true;
		}
		if(i>0) url += "&";
		url += token[i];
	}
	if(!found)
		url += "&" + var_name + "=" + new_value;
	//alert(url);
	document.location = url;
}