title: Get parent SKU (configurable or bundle) from child SKU
body: <p>On the cart page I need to be able to obtain the parent SKU using a child SKU.</p>
  
  <p>I've tried several code snipped from both the Magento forums and similar questions here on StackOverflow without success. </p>
  
  <p>I'm able to determine if a product is just a simple product without a parent by using getTypeId() but after that everything I try fails to result in getting at the parent SKU. </p>
  
  <p>Magento Version: 1.4.2.0</p>