* prelude.rb: add Thread.exclusive. This class method

is different from 1.8's.  Thread.exclusive only does
  synchronize with VM global mutex.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@13257 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

prelude.rb

@@ -10,3 +10,14 @@ class Mutex
   end
 end
 
+# Thread
+
+class Thread
+  MUTEX_FOR_THREAD_EXCLUSIVE = Mutex.new
+  def self.exclusive
+    MUTEX_FOR_THREAD_EXCLUSIVE.synchronize{
+      yield
+    }
+  end
+end
+