changed the behavior of Thread

-- removed Thread.getStatus()
-- removed addEventListener, removeEventListener, dispatchEvent, postMessage
-- added constants Thread.RUNNING, Thread.TERMINATED, Thread.ERROR
-- status now returns 1, 2 or 3 (look at the new constants)
-- added Thread.id and Thread.group_id
-- added Thread.send
-- now using strict mode
-- added ThreadGroup
-- all threads now belong to a ThreadGroup, not more, not less
-- every thread source must now be enclosed in a anonymous function
-- Thread now throws an exception on error