rb_ensure is insufficient cleanup for fork and we must
reinitialize all waitqueues in the child process.
Unfortunately this increases the footprint of ConditionVariable,
Queue and SizedQueue by 8 bytes on 32-bit (16 bytes on 64-bit).
[ruby-core:86316] [Bug #14634]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62934 b2dd03c8-39d4-4d8f-98ff-823fe69b080e