title: Add an extra argument to capistrano
body: <p>I'm trying to add an extra argument to Capistrano so we can query a central server via API to get the target:</p>
  <pre><code>cap production deploy target
  </code></pre>
  <p>Everything works great, target is preprocessed (in config/deploy/production.rb) and the correct server is found via API (determined by target), and the deploy completes successfully. However, at the end of the deploy, I get an error:</p>
  <p>(Backtrace restricted to imported tasks)
  cap aborted!
  Don't know how to build task 'target' (See the list of available tasks with <code>cap --tasks</code>)</p>
  <pre><code>(See full trace by running task with --trace)
  The deploy has failed with an error: Don't know how to build task 'target' (See the list of available tasks with `cap --tasks`)
  </code></pre>
  <p>Is there any way to get rid of this error?</p>
  <p>FYI, the way we use the 3rd argument (target) in production.rb is to use ARGV, then we do a lookup to a central server with HTTParty.  The idea is that we need to deploy to 20+ servers and rather than have one deploy file for each new server, just use an API to get the targets.</p>
  <p>Thanks for any help,
  Kevin</p>