function login_with_email_address($username) {
    $user = get_user_by('email',$username);
    if(!empty($user->user_login))
        $username = $user->user_login;
    return $username;
}
add_action('wp_authenticate','login_with_email_address');
function change_username_wps_text($text){
       if(in_array($GLOBALS['pagenow'], array('wp-login.php'))){
         if ($text == 'Username'){$text = 'Username / Email';}
            }
                return $text;
         }
add_filter( 'gettext', 'change_username_wps_text' );