Reduced the number of Iterator to ArrayBuffer copies in NetworkReceiver.
Remove SIGCHLD handler in PySpark workers so pipe() works
Moved Kafka methods to a wrapper class and other streaming fixes

- The Kafka methods were moved because referencing a kafka.* type in a
  method of StreamingContext required all Spark Streaming apps to link
  to Kafka

- Also fixed some input streams that were not being stored on disk and
  some non-ASCII characters