ripper lib not supported on jruby

[webframp]

JRuby 1.7.2, Found this testing out flycheck:

Checker ruby-rubocop returned non-zero exit code 1, but no errors from output: the `ripper' lib is not supported on JRuby
LoadError: no such file to load -- ripper
  require at org/jruby/RubyKernel.java:1027
  require at /home/sme/.rbenv/versions/jruby-1.7.2/lib/ruby/shared/rubygems/custom_require.rb:36
   (root) at /home/sme/.rbenv/versions/jruby-1.7.2/lib/ruby/1.9/ripper/core.rb:11
  require at org/jruby/RubyKernel.java:1027
   (root) at /home/sme/.rbenv/versions/jruby-1.7.2/lib/ruby/shared/rubygems/custom_require.rb:1
  require at /home/sme/.rbenv/versions/jruby-1.7.2/lib/ruby/shared/rubygems/custom_require.rb:36
  require at org/jruby/RubyKernel.java:1027
   (root) at /home/sme/.rbenv/versions/jruby-1.7.2/lib/ruby/1.9/ripper.rb:3
   (root) at /home/sme/.rbenv/versions/jruby-1.7.2/lib/ruby/shared/rubygems/custom_require.rb:1
  require at org/jruby/RubyKernel.java:1027
  require at /home/sme/.rbenv/versions/jruby-1.7.2/lib/ruby/shared/rubygems/custom_require.rb:36
   (root) at /home/sme/.rbenv/versions/jruby-1.7.2/lib/ruby/gems/shared/gems/rubocop-0.6.1/bin/../lib/rubocop.rb:3
     load at org/jruby/RubyKernel.java:1046
   (root) at /home/sme/.rbenv/versions/jruby-1.7.2/lib/ruby/shared/rubygems/custom_require.rb:1

Checker definition probably flawed.

1.9 mode is the default, so I wouldn't expect ripper to even be needed. Likely just a jruby issue, but reporting for tracking anyway.

[bbatsov]

RuboCop depends on the ripper library, that's MRI specific. I guess we might fail more gracefully on JRuby and Rubinius, though.