title: Rails 2 - Absolute of money
body: <p>How to get absolute value of money?
  e.g:</p>
  
  <pre><code>-2.to_money.? = 2.to_money
   2.to_money.? = 2.to_money
  </code></pre>
  
  <p>I have an attribute <strong>total_price</strong>, which may be positive or negative. I want to calculate the absolute value of total_price.</p>