* lib/rubygems/compatibility.rb:  Hide compatibility shims from RDoc

* lib/rubygems/config_file.rb:  Hide RbConfig use from RDoc

* lib/rubygems/test_case.rb:  Added note to use realpath when 1.8
  support is dropped.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38932 b2dd03c8-39d4-4d8f-98ff-823fe69b080e