Apache license headers and RAT

[Grant Ingersoll]

Just a reminder, you can check to make sure all new files have the  
proper headers by running "ant rat-sources" from the top.  You will  
need the RAT JAR files in your Ant lib.  See https://issues.apache.org/jira/browse/SOLR-762 
 and http://incubator.apache.org/rat/

-Grant