* Fixed race conditions in Timed_Executor that were caused by using non-thread safe managed memory via Compiled_Expression in the Timed_Executor and Timed_Event_Thread classes
  * The changes do not make Compiled_Expression thread safe--such changes would make the entire knowledge engine much slower. Instead, we simply do not use Compiled_Expression and understand that the Thread_Safe_Context destructor will clear the interpreter cache of expressions, and that we really shouldn't be doing refcounted compiled expressions in the threads
* Added evaluate for rooted-tree to the knowledge engine, in addition to strings and Compiled_Expression
* Added tutorial for using the timed executor and timed event threads
* Updated to version 1.5.3

git-svn-id: http://madara.googlecode.com/svn/trunk@1209 2850746a-f1c8-11dd-b507-8b4ecd5210be