Move genhash to contrib

This isn't part of the core

Change-Id: Ida0a40df2c811de05e4ee9b6cd8811b3ef5bc4eb
Reviewed-on: http://review.couchbase.org/39385
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>