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.
svn merge --ignore-ancestry -c 1529229 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1529230 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/branch-2' into branch-2-gd
Merge remote branch 'origin/branch-2-gd' into fb-MAPREDUCE-4884-branch-2-gd