source http://hadoop.apache.org/common/docs/current/mapred_tutorial.html
 javac -classpath /usr/lib/hadoop/hadoop-0.20.2-cdh3u1-core.jar -d wordcount_classes WordCount.java
 mkdir wordcount_classes
 jar -cvf wordcount.jar -C wordcount_classes/ .
 hadoop jar wordcount.jar org.myorg.WordCount in/infile out/outfile