title: Gem dependencies with Rails 3 engine fail in initializer
body: <p><strong>tldr; When I run a rake task in a test app which uses an Engine, the Engine dependencies don't seem to be respected. I have to (-D)RY by specifying the dependency in the test app's Gemfile</strong></p>
  
  <p>I've created a Rails Engine as a gem using Jeweler. It has a dependency on Devise which I've specified in the Rakefile:</p>
  
  <pre><code>gem.add_runtime_dependency 'devise', '~&gt; 1.1.3'
  </code></pre>
  
  <p>In my test app I add the Engine dependency to the Gemfile, and <code>bundle install</code> shows that Devise is picked up and installed. However if I run an initial <code>rake db:migrate</code> an error is thrown:</p>
  
  <pre><code>uninitialized constant Devise
  &lt;snip&gt;config/initializers/devise.rb:3
  </code></pre>
  
  <p>If I manually add the Devise dependency to the test app's Gemfile it works. I've probably missed something obvious, but at this stage it appears the test app picks up and installs the dependency properly, but for some reason the initializer code fails unless the dependency is listed again in the test app's Gemfile.</p>