Ответ 1
Оберните свой код в <div class="dropdown">
(Пример)
<td>
<div class="dropdown">
<button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">Action <span class="caret"></span></button>
<ul class="dropdown-menu" role="menu" >
<li class="dropdown"><a href="#">Edit</a></li>
<li class="dropdown"><a href="warga/delete/<?php echo $a->id;?>">Delete</a></li>
</ul>
</div>
</td>