title: rubyonrails error when update to gem 1.8.1
body: <p>I update gem to the latest 1.8.1
  and now when i use rails command
  i got errors as below</p>
  
  <pre><code>NOTE: Gem::Specification#default_executable= is deprecated with no replacement. 
  It will be removed on or after 2011-10-01.
  Gem::Specification#default_executable= called from /Library/Ruby/Gems/1.8/specifications/rubygems-update-1.7.2.gemspec:11.
  NOTE: Gem::Specification#default_executable= is deprecated with no replacement. It will be removed on or after 2011-10-01.
  Gem::Specification#default_executable= called from /Users/Haxrat/.gem/ruby/1.8/specifications/RedCloth-4.2.7.gemspec:10.
  </code></pre>