Give users a clue how they called it.
explicitly set java source and target to 1.6 for the ant tasks
patch by dbrosius reviewed by slebresne for CASSANDRA-5533
Merge branch 'cassandra-1.0' into cassandra-1.1
explicitly set java source and target to 1.6 for the ant tasks
Merge branch 'cassandra-1.1' into cassandra-1.2