upgrades RedCloth dependency to ~> 4.2, adds RedCloth to the project's Rakefile, removes gem call from the guides generator (use bundle exec if needed)

Gemfile

@@ -14,6 +14,7 @@ gem "rake",  ">= 0.8.7"
 gem "mocha", ">= 0.9.8"
 gem "rdoc",  "~> 3.4"
 gem "horo",  "= 1.0.3"
+gem "RedCloth", "~> 4.2"
 
 # for perf tests
 gem "faker"

railties/guides/rails_guides.rb

@@ -24,14 +24,14 @@ rescue LoadError
 end
 
 begin
-  gem 'RedCloth', '>= 4.1.1'
   require 'redcloth'
 rescue Gem::LoadError
+  # This can happen if doc:guides is executed in an application.
   $stderr.puts('Generating guides requires RedCloth 4.1.1+.')
   $stderr.puts(<<ERROR) if bundler?
 Please add
 
-  gem 'RedCloth', '>= 4.1.1'
+  gem 'RedCloth', '~> 4.2'
 
 to the Gemfile, run
 

railties/guides/source/contribute.textile

@@ -13,8 +13,8 @@ h3. How to Contribute?
 * Assets are stored in the +railties/guides/assets+ directory.
 * Sample format : "Active Record Associations":http://github.com/lifo/docrails/blob/3e56a3832415476fdd1cb963980d0ae390ac1ed3/railties/guides/source/association_basics.textile.
 * Sample output : "Active Record Associations":association_basics.html.
-* You can build the Guides during testing by running +rake generate_guides+ in the +railties+ directory.
-* You're encouraged to validate XHTML for the generated guides before commiting your changes by running +rake validate_guides+ in the +railties+ directory.
+* You can build the Guides during testing by running +bundle exec rake generate_guides+ in the +railties+ directory.
+* You're encouraged to validate XHTML for the generated guides before commiting your changes by running +bundle exec rake validate_guides+ in the +railties+ directory.
 * Edge guides "can be consulted online":http://edgeguides.rubyonrails.org/. That website is generated periodically from docrails.
 
 h3. What to Contribute?

railties/guides/source/ruby_on_rails_guides_guidelines.textile

@@ -45,7 +45,7 @@ h3. HTML Generation
 To generate all the guides just cd into the +railties+ directory and execute
 
 <plain>
-rake generate_guides
+bundle exec rake generate_guides
 </plain>
 
 You'll need the gems erubis, i18n, and RedCloth.
@@ -53,7 +53,7 @@ You'll need the gems erubis, i18n, and RedCloth.
 To process +my_guide.textile+ and nothing else use the +ONLY+ environment variable:
 
 <plain>
-rake generate_guides ONLY=my_guide
+bundle exec rake generate_guides ONLY=my_guide
 </plain>
 
 Although by default guides that have not been modified are not processed, so +ONLY+ is rarely needed in practice.