Fixes :nodoc: on class aliases. Fixes :stopdoc: creating references
to Object. Fixes spacing when class comments are merged in ri.
Fixes `ri []` crash. Fixes bug report URL when rdoc crashes. Adds
:doc: and :nodoc: to allow hiding of implementation details in ruby.
Makes `rdoc` and `ri` gem-aware.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_3@32868 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
