CCBC-436: Allow more robust checks for exists of ctls

This implements the missing compmode handler and adds a test to ensure
that all control codes actually exist.

Change-Id: I4fb42382bc472c6c13f0457799dbf09d3f0a96f6
Reviewed-on: http://review.couchbase.org/37789
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>