Added the possibility to render append/prepend without a span wrap

Can be used like this:
<h4>Example 1</h4>
```php
echo $form->textFieldRow($model, 'url', array(
	'appendOptions' => array('isRaw' => true), 
	'append' => $this->widget('bootstrap.widgets.TbButton', array('label' => 'Make url'), true),
));
```
<h4>Example 2</h4>
```php
echo $form->textFieldRow($model, 'url', array(
	'appendOptions' => array('isRaw' => true), 
	'append' => $this->renderPartial('parts/_btn_makeurl',null,true)
));
```
contents of _btn_makeurl.php
```php

<?php $this->widget('bootstrap.widgets.TbButton', array('label' => 'Make url')); ?>
```
![booster-add2](https://f.cloud.github.com/assets/3715881/326334/b6be92a4-9b2e-11e2-8cb0-b95572c09e27.png)

More examples from twitter bootsrap
![booster-add](https://f.cloud.github.com/assets/3715881/326332/8870b940-9b2e-11e2-8c76-4fc0541885ce.png)