title: Rake assets:precompile fails with: couldn't find file 'handlebars'
body: <p>Running the command during a capistrano deploy:</p>
  
  <pre><code>bundle exec rake RAILS_ENV=staging RAILS_GROUPS=assets assets:precompile
  </code></pre>
  
  <p>returns</p>
  
  <pre><code>rake aborted!
  couldn't find file 'handlebars'
  (in */app/assets/javascripts/application.js:22)
  */ruby/1.9.1/gems/sprockets-2.2.2/lib/sprockets/context.rb:102:in `resolve'
  */ruby/1.9.1/gems/sprockets-2.2.2/lib/sprockets/context.rb:142:in `require_asset'
  *************
  Tasks: TOP =&gt; assets:precompile:all
  </code></pre>
  
  <p>Gem ember-rails is in a global scope in my Gemfile and I am using handlebars-source (1.0.12), ember-rails (0.12.0), ember-source (1.0.0.rc6.2) in Rails 3.2.12 and ruby 1.9.3.
  It's probably worth noting that this works in production, but not in staging deploys.</p>
  
  <p>Also I have the following in my staging.rb, which appears to be the common issue.</p>
  
  <pre><code>config.ember.variant = :production
  </code></pre>