MAPREDUCE-5137. AM web UI: clicking on Map Task results in 500 error. Contributed by Thomas Graves


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1466948 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk-gd
Merge remote branch 'origin/trunk-gd' into fb-HDFS-4312-trunk-gd