Update release metadata for 2.4.0-dp1

This bumps up the 'revision' ABI number to 16. The previous was 14, but
a prospective 2.3.2 will be 15

Change-Id: I463a769849aae62868e11f69dbe2d00e0dd80a4b
Reviewed-on: http://review.couchbase.org/38571
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Matt Ingenthron <matt@couchbase.com>