title: upgrading to ruby 1.9.3 with rvm breaks my rails app
body: <p>I have upgraded ruby using the following commands with rvm:</p>
  
  <pre><code>rvm get head
  rvm install 1.9.3
  rvm reload
  rvm use 1.9.3 --default
  </code></pre>
  
  <p>Now when I run rails s I get the following error message:</p>
  
  <pre><code>/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems.rb:827:in `report_activate_error': Could not find RubyGem rails (&gt;= 0) (Gem::LoadError)
  from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems.rb:261:in `activate'
  from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems.rb:68:in `gem'
  from /usr/bin/rails:18
  </code></pre>
  
  <p>If I run which ruby, gem environment, and ruby -v I get coherent output. Could anyone help me understand what is going wrong with my application? </p>