More test code added...

More test code added...
     more bugs found

facebook::thrift::concurrency::ThreadManager::add
	Fixed dispatch error that resulted in only one of N worker threads ever getting notified of work

facebook::thrift::concurrency::ThreadManager
	Cleaned up addWorker/removeWorker and stop logic so that adding/removing workers doesn't wake up
	all blocked workers.

facebook::thrift::concurrency::Thread
facebook::thrift::concurrency::Runnable
	Fixed initialization logic so that runnable can return the thread that runs it

git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@664729 13f79535-47bb-0310-9956-ffa450edef68