merges r22091 from trunk into ruby_1_9_1.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_1@22517 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
merges r22091 from trunk into ruby_1_9_1.
It fails on OpenBSD 4.4 when pthread library is linked.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_1@22517 b2dd03c8-39d4-4d8f-98ff-823fe69b080e