* gem_prelude.rb (Gem.path): uses Gem.default_path as a default value
  so that ruby finds gems in ~/.gem/.
  (Gem.user_home): reduced version of lib/rubygems.rb's.
  Gem.default_path needs it.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@24328 b2dd03c8-39d4-4d8f-98ff-823fe69b080e