Add a TODO about not mutating the Txn directly.
Add a TODO about not mutating the Txn directly.

sunya123/cockroach,veteranlu/cockroach,glycerine/cockroach,maxlang/cockroach,arjun4084346/cockroach,cuongdo/cockroach,glycerine/cockroach,nieyy/cockroach,petermattis/cockroach,bg451/cockroach,vivekmenezes/cockroach,cockroachdb/cockroach,arjun4084346/cockroach,cockroachdb/cockroach,paperstreet/cockroach,veteranlu/cockroach,glycerine/cockroach,nieyy/cockroach,bg451/cockroach,cuongdo/cockroach,sunya123/cockroach,il9ue/cockroach,nieyy/cockroach,sunya123/cockroach,cockroachdb/cockroach,petermattis/cockroach,paperstreet/cockroach,arjun4084346/cockroach,bg451/cockroach,vaibhavarora/cockroach,bg451/cockroach,arjun4084346/cockroach,sunya123/cockroach,il9ue/cockroach,sunya123/cockroach,vaibhavarora/cockroach,il9ue/cockroach,bg451/cockroach,veteranlu/cockroach,cuongdo/cockroach,vaibhavarora/cockroach,glycerine/cockroach,vivekmenezes/cockroach,nieyy/cockroach,petermattis/cockroach,sunya123/cockroach,maxlang/cockroach,arjun4084346/cockroach,petermattis/cockroach,vivekmenezes/cockroach,paperstreet/cockroach,sunya123/cockroach,arjun4084346/cockroach,veteranlu/cockroach,paperstreet/cockroach,paperstreet/cockroach,glycerine/cockroach,maxlang/cockroach,il9ue/cockroach,vaibhavarora/cockroach,maxlang/cockroach,il9ue/cockroach,arjun4084346/cockroach,maxlang/cockroach,vaibhavarora/cockroach,nieyy/cockroach,sunya123/cockroach,cuongdo/cockroach,nieyy/cockroach,cockroachdb/cockroach,paperstreet/cockroach,cockroachdb/cockroach,vaibhavarora/cockroach,bg451/cockroach,petermattis/cockroach,vivekmenezes/cockroach,vivekmenezes/cockroach,glycerine/cockroach,petermattis/cockroach,veteranlu/cockroach,paperstreet/cockroach,cuongdo/cockroach,vivekmenezes/cockroach,veteranlu/cockroach,maxlang/cockroach,veteranlu/cockroach,il9ue/cockroach,cockroachdb/cockroach,vaibhavarora/cockroach,maxlang/cockroach,maxlang/cockroach,paperstreet/cockroach,cuongdo/cockroach,cuongdo/cockroach,il9ue/cockroach,bg451/cockroach,vaibhavarora/cockroach,vivekmenezes/cockroach,glycerine/cockroach,cockroachdb/cockroach,nieyy/cockroach,arjun4084346/cockroach,glycerine/cockroach,il9ue/cockroach,veteranlu/cockroach,vivekmenezes/cockroach,petermattis/cockroach,cockroachdb/cockroach,cuongdo/cockroach,petermattis/cockroach,nieyy/cockroach