gem activation does not work by default. Now it can be worked
around by requiring "rubygems" first. [ruby-core:29486]
a patch from Evan Phoenix in [ruby-core:31096].
* lib/rubygems.rb: ditto.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@28570 b2dd03c8-39d4-4d8f-98ff-823fe69b080e