title: Recompile Heroku slug without push or config change
body: <p>I'm wondering if there is a way to force Heroku to recompile the slug without pushing new commits and/or updating the config variables.</p>
  
  <p>Why would I want to do this?:</p>
  
  <p>I am using the Cedar stack on Heroku for a Rails 3.2 app, and I am having problems with the <code>rake assets:precompile</code> task failing (during compilation only --- later it works fine with a <code>heroku run</code>).  I highly suspect this is due to certain environment variables not being available during slug compilation time, and I think the <code>heroku labs:enable user_env_compile</code> experimental feature will solve this. </p>
  
  <p>However, with the <code>user_env_compile</code> feature turned on, config changes do not trigger a recompilation of the slug, and my code hasn't changed, so I don't have any new commits to push.</p>
  
  <p>Of course, I could push a "dummy" commit with a trivial change, which is probably the simplest answer --- but I'm wondering if there's a heroku command that will let me directly recompile the slug.</p>
  
  <p>Thanks!</p>