Sync output message

* sync $stdout to ensure outputting on expected SEGV.
  this caused failure:
  http://u64.rubyci.org/~chkbuild/ruby-trunk/log/20130121T230101Z.log.html.gz
* check result of invoke_ruby
* use assert_operator

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38893 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2013-01-22

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38894 b2dd03c8-39d4-4d8f-98ff-823fe69b080e