merges r20210 from trunk into ruby_1_9_1.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_1@20221 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
merges r20210 from trunk into ruby_1_9_1.
a patch from Wataru Kimura in Bug #193 [ruby-core:17333].
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_1@20221 b2dd03c8-39d4-4d8f-98ff-823fe69b080e