FLUME-299: Add support for subarguments in flume config elements

Review Request #1757 - Created May 21, 2011 and submitted

Jonathan Hsieh
esammer, todd
This updates the grammar to support "functions" with subargs.  Initial goal is support compression sub-arguments to avro/seqfile, but will also be used for roll triggers and other things in the future.

This is related to flume-420, with the end goal of supporting flume-632.
test run and pass.
  1. I left a comment on the JIRA to open a larger discussion, but lgtm. I see k has been increased which probably speaks to the risk of ambiguities in the grammar. We should revisit.
  2. nit: would be nice if this was slightly more descriptive (i.e. was FUNCTION). we all know flume is fun...