Form_Basic: extend addSeparator
Form_Basic: extend addSeparator

With this extension we can set at least some new attributes to fieldsets with addSeparator.
For example,
```
$form->addSeparator('span6',array('id'='foo','style'='color:red'));
```

samratcis/atk4,xepan/atk4,atk4/atk4,samratcis/atk4,svisystem/atk4,xepan/atk4,atk4/atk4,atk4/atk4,svisystem/atk4,svisystem/atk4,atk4/atk4,xepan/atk4,samratcis/atk4