PYCBC-213: Add interfaces for lcb_cntl

These _private_ interfaces are added to provide workarounds for settings
not directly exposed by the API via lcb_cntl

Change-Id: I63374347c8f8df9cd43aa8ed81f0d0d3cf1101d9
Reviewed-on: http://review.couchbase.org/31675
Reviewed-by: Matt Ingenthron <matt@couchbase.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>