Validate the datatype
Validate the datatype

Don't accept a non-null datatype for clients who haven't
asked for it

Change-Id: I9ad2e222e66ce0edbc47ec0a728c712ea0538b60
Reviewed-on: http://review.couchbase.org/34932
Tested-by: buildbot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Trond Norbye <60edd2ef23891a753f231b0c6f161dc634079a93@gmail.com>

owendCB/memcached,daverigby/kv_engine,mrkwse/memcached,owendCB/memcached,couchbase/memcached,daverigby/memcached,daverigby/memcached,jimwwalker/memcached,daverigby/memcached,daverigby/memcached,owendCB/memcached,owendCB/memcached,jimwwalker/memcached,daverigby/kv_engine,mrkwse/memcached,daverigby/kv_engine,cloudrain21/memcached-1,mrkwse/memcached,jimwwalker/memcached,couchbase/memcached,daverigby/kv_engine,couchbase/memcached,cloudrain21/memcached-1,mrkwse/memcached,couchbase/memcached,cloudrain21/memcached-1,cloudrain21/memcached-1