After APPEND/PREPEND to json, set datatype to binary

This is because appending or prepending anything
to a JSON document breaks the JSON structure.

Change-Id: I0acd99b0c43a54e0b34ce21f3a69c41709e3817e
Reviewed-on: http://review.couchbase.org/40390
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: abhinav dangeti <abhinav@couchbase.com>