function check_files(id,filter)
{
     var fup = document.getElementById(id);
     var fileName = fup.value;
     var ext = fileName.substring(fileName.lastIndexOf('.') + 1);
     var filterarr = filter.split(',');
     for (var i=0; i<filterarr.length;i++)
     {
        if (ext.toLowerCase()==filterarr[i])
        return true;
     } 
    fup.value='';    
    fup.focus();
    return false;      
}