Fixed documentation generation when sdoc and json are installed as
gems.
Added some missing documentation.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43317 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
Fixes building extensions without a "clean" make rule
Adds gem dependency file autodetection to "gem install -g"
* test/rubygems: Tests for the above.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43299 b2dd03c8-39d4-4d8f-98ff-823fe69b080e