merges r20615 from trunk into ruby_1_9_1.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_1@20693 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
merges r20615 from trunk into ruby_1_9_1.
Kazuhiro NISHIYAMA in [ruby-dev:37345]. fix #846
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_1@20693 b2dd03c8-39d4-4d8f-98ff-823fe69b080e