title: Magento: How to filter current category by another category - layered navigation
body: <p>I have a Magento (1.7.0.2) installation with some products inside.
  I have two sibling categories (Brand and Clothes).
  Brand contains all the brands of the clothes, and clothes have multiple subcategories (shoes, pants, etc.)
  I am using layered navigation. When opening a category (lets say "shoes"), I display a list of the brands in the layered navigatin (I wrote some custom code for this).</p>
  
  <p>Here is the problem:
  When I click on a brand, I want magento to filter the products by both categories and display matching results.
  Since Magento's default functionality is to just display items from the last category clicked, I need to change this.</p>
  
  <p>Does anyone have any ideas how ?</p>