title: ReWrite rule to add .html extension
body: <p>I need a rule that will add an .html extension whenever there is 'not' a trailing slash.</p>
  
  <p>A new client recently changed ecommerce scripts and the new version handles SEO differently and changed all of their 16,000+ product links. This was not caught prior to the site being re-indexed so we need to redirect the old to the new..</p>
  
  <p>All products used to have links like this
  domain.com/category/productname
  but are now
  domain.com/category/productname.html</p>
  
  <p>Category links did not change and all are like this
  domain.com/category/ (with trailing slash)</p>