rdoc, ri, rdoc-data and 'generate-ri-cache' ant task

We have a few problems concerning the rdoc, ri documentation.

1. dist target installs rdoc and ri into bin. The scripts rely on RubyGems to provide the respective gems, but we do not distribute them. Thus, for the binary package we get:

   [system] jruby-1.7.0.dev $ ./bin/jruby -S ri String
   Gem::LoadError: Could not find rdoc (>= 0) amongst [rake-0.9.2.2]
     to_specs at /Users/asari/Downloads/jruby-1.7.0.dev/lib/ruby/shared/rubygems/dependency.rb:247
      to_spec at /Users/asari/Downloads/jruby-1.7.0.dev/lib/ruby/shared/rubygems/dependency.rb:256
          gem at /Users/asari/Downloads/jruby-1.7.0.dev/lib/ruby/shared/rubygems.rb:1202
       (root) at /Users/asari/Downloads/jruby-1.7.0.dev/bin/ri:18
   

2. When you install rdoc, you get the following message (in both 1.8 and 1.9 modes):

   [system] jruby-1.7.0.dev $ ./bin/jruby --1.9 -S gem install rdoc
   Fetching: json-1.6.5-java.gem (100%)
   Fetching: rdoc-3.12.gem (100%)
   Depending on your version of ruby, you may need to install ruby rdoc/ri data:
   
   <= 1.8.6 : unsupported
    = 1.8.7 : gem install rdoc-data; rdoc-data --install
    = 1.9.1 : gem install rdoc-data; rdoc-data --install
   >= 1.9.2 : nothing to do! Yay!
   Successfully installed json-1.6.5-java
   Successfully installed rdoc-3.12
   2 gems installed
   

   It is not clear what the user is supposed to do for JRuby. The answer is that you need to install rdoc-data, and run the indicated command. If the marginal storage is negligible, it might be best to distribute these gems (rdoc and rdoc-data) and run rdoc-data --install beforehand for the dist target to avoid this potential confusion.

3. Right now, generate-ri-cache ant task is commented out in build.xml. This task fails because of the issues described above.