title: jQuery failure in javascript_include_tag during migration to Rails 3.1
body: <p>I am trying to migrate an application from Rails 3 to 3.1 and having problems with jQuery. The error is bellow. If I remove 'javascript_include_tag "application"' all works fine (with no javascript), so something javascript-related is missing.</p>
  
  <pre><code>Showing C:/.../app/views/layouts/application.html.erb where line #7 raised:
  
  couldn't find file 'jquery'
    (in C:/.../app/assets/javascripts/application.js:7)
   Extracted source (around line #7):
  
  4:   &lt;title&gt;&lt;%= @title unless @title.blank? %&gt;&lt;/title&gt;
  5:   &lt;!-- %= render 'layouts/stylesheets' % --&gt; 
  6:   &lt;%= stylesheet_link_tag "application" %&gt;
  7:   &lt;%= javascript_include_tag "application", :debug =&gt; true %&gt;
  8:   &lt;%= csrf_meta_tags %&gt;
  9: &lt;/head&gt;
  10: &lt;body&gt;
  </code></pre>
  
  <p>In my Gemfile I have the entry for jquery-rails:</p>
  
  <pre><code>source 'http://rubygems.org'
  
  gem 'rails', '3.1.0'
  gem 'jquery-rails'
  ....
  </code></pre>
  
  <p>In application.js:</p>
  
  <pre><code>// This is a manifest file .......
  //
  //= require jquery
  //= require jquery_ujs
  //= require_tree .
  //
  </code></pre>
  
  <p>As far as I know that it is the only requirement for working with jQuery in Rails 3.1.</p>
  
  <p>What am I missing?</p>