rbinstall.rb: show categories of default gems
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60578 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
rbinstall.rb: show categories of default gems
default gems, pure ruby libraries and libraries with extensions.
[ruby-core:83600] [Bug #14065]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60578 b2dd03c8-39d4-4d8f-98ff-823fe69b080e