Fix build failure of sample/Thread on OS X 10.9

git-svn-id: https://svn.code.sf.net/p/rubycocoa/svn/trunk/src@2583 f4f36d40-9719-0410-9868-dde021a23eda
Fix sample apps using ruby Thread do not work with ruby-2.x

add missing `Thread.pass`.

git-svn-id: https://svn.code.sf.net/p/rubycocoa/svn/trunk/src@2584 f4f36d40-9719-0410-9868-dde021a23eda