MAPREDUCE-5533. Fixed MR speculation code to track any TaskAttempts that aren't heart-beating for a while, so that we can aggressively speculate instead of waiting for task-timeout. Contributed by Xuan Gong.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1529229 13f79535-47bb-0310-9956-ffa450edef68