title: Customize requestFinished, requestFailed conditions for ASIHTTPRequest
body: <p>I would like to customize <code>ASIHTTPRequest</code> to be more picky about when it fires <code>requestFinished</code>. In particular, I <em>only</em> want <code>requestFinished</code> to be called when the status code is <code>200</code>. Other than that, for all other status codes, or network-level failures, I want a <code>requestFailed</code>. Is there a way to override the default functionality cleanly, or am I opening a can of worms by trying to modify <code>ASIHTTPRequest</code>? If there is a way to do it cleanly, where is it?</p>