Restore changelogs to 2.3.1 versions

Change-Id: I4a78371daf1f4e65b954c7682a4c4d63a4352552
Reviewed-on: http://review.couchbase.org/38626
Reviewed-by: Matt Ingenthron <matt@couchbase.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>