title: NSDecimalNumber issues
body: <p>In my iOS swift application, I receive some json from the web which contains some double values which represent currency. It looks like this:</p>
  
  <pre><code>[{"Amount": 5.0},{"Amount":-26.07},{"Amount": 4}, ...etc]
  </code></pre>
  
  <p>I cast these as Doubles and then try to feed these values as a Swift "Double" into the NSDecimalNumber's constructor like this:</p>
  
  <pre><code>let amount = NSDecimalNumber(double: amountAsDouble)
  </code></pre>
  
  <p>I'm running into problems with this approach because very frequently the NSDecimalNumber I created will contain a different number that goes 16 places passed the decimal point.</p>
  
  <pre><code>let amount = NSDecimalNumber(double: -15.97)
  println(amount)
  </code></pre>
  
  <p>this returns -15.970000000000004096</p>
  
  <p>I don't want this, I want -15.97.
  Thanks,</p>