title: Jekyll plugins not recognized
body: <p>I'm trying to reproduce the Jekyll plugin example from <a href="https://github.com/mojombo/jekyll/wiki/Plugins" rel="nofollow">https://github.com/mojombo/jekyll/wiki/Plugins</a> to render the *render_time* tag, but I get this error:</p>
  
  <pre><code>/Library/Ruby/Gems/1.8/gems/liquid-2.0.0/lib/liquid/block.rb:58:in `unknown_tag': Unknown tag 'render_time' (Liquid::SyntaxError)
  from /Library/Ruby/Gems/1.8/gems/liquid-2.0.0/lib/liquid/block.rb:28:in `parse'
  from /Library/Ruby/Gems/1.8/gems/liquid-2.0.0/lib/liquid/document.rb:5:in `initialize'
  from /Library/Ruby/Gems/1.8/gems/liquid-2.0.0/lib/liquid/template.rb:58:in `new'
  from /Library/Ruby/Gems/1.8/gems/liquid-2.0.0/lib/liquid/template.rb:58:in `parse'
  from /Library/Ruby/Gems/1.8/gems/liquid-2.0.0/lib/liquid/template.rb:46:in `parse'
  from /Library/Ruby/Gems/1.8/gems/jekyll-0.5.7/bin/../lib/jekyll/convertible.rb:72:in `do_layout'
  from /Library/Ruby/Gems/1.8/gems/jekyll-0.5.7/bin/../lib/jekyll/page.rb:79:in `render'
  from /Library/Ruby/Gems/1.8/gems/jekyll-0.5.7/bin/../lib/jekyll/site.rb:158:in `render'
  from /Library/Ruby/Gems/1.8/gems/jekyll-0.5.7/bin/../lib/jekyll/site.rb:154:in `each'
  from /Library/Ruby/Gems/1.8/gems/jekyll-0.5.7/bin/../lib/jekyll/site.rb:154:in `render'
  from /Library/Ruby/Gems/1.8/gems/jekyll-0.5.7/bin/../lib/jekyll/site.rb:99:in `process'
  from /Library/Ruby/Gems/1.8/gems/jekyll-0.5.7/bin/jekyll:129
  from /usr/bin/jekyll:19:in `load'
  from /usr/bin/jekyll:19
  </code></pre>
  
  <p>I've got my plugin in *./_plugins/homepage.rb* and the _config.yml contains the standard rules:</p>
  
  <pre><code>source:      .
  destination: ./_site
  plugins:     ./_plugins
  </code></pre>
  
  <p>Anyone with the same issue?</p>