//---------
// select/deselect all checkboxes
//---------
var isAlertsChecked = false;
function checkAll(field) 
{
    var i;
    if(!isAlertsChecked)
    {
	    for(i=0; i<field.length; i++)
	    {
			field[i].checked = true;
			isAlertsChecked = true;
	    }
	}
	else
	{
	    for(i=0; i<field.length; i++)
	    {
			field[i].checked = false;
			isAlertsChecked = false;
	    }	
	}
}