Don't incref mresult

This fixes some serious memory leaks whenever a store operation is
executed

Change-Id: I07e04c5532ed19aff0d9832b1f216e1f26d96863
Reviewed-on: http://review.couchbase.org/26656
Reviewed-by: Mordechai Nunberg <mnunberg@haskalah.org>
Tested-by: Mordechai Nunberg <mnunberg@haskalah.org>