thread.c: Update documents
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60885 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
thread.c: Update documents
data structures for branch coverage.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60885 b2dd03c8-39d4-4d8f-98ff-823fe69b080e