HADOOP-2574. import for FileUtil was missing in 0.15.

git-svn-id: https://svn.apache.org/repos/asf/lucene/hadoop/branches/branch-0.15@611871 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/hadoop/mapred/TaskTracker.java

@@ -52,6 +52,7 @@ import org.apache.hadoop.fs.FSError;
 import org.apache.hadoop.fs.FileStatus;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.fs.FileUtil;
 import org.apache.hadoop.fs.LocalDirAllocator;
 import org.apache.hadoop.io.IntWritable;
 import org.apache.hadoop.ipc.RPC;