Add "trace{on,off}" commands.
Add "trace{on,off}" commands.

This allows tracing to be enabled for individual SQL operations which is
useful for performance analysis. Use by creating a file containing an
operation to trace:

    statement ok
    CREATE TABLE t (k INT PRIMARY KEY)

    statement ok
    INSERT INTO t VALUES (1)

    traceon trace.out

    query I
    SELECT * FROM t
    ----
    1

    traceoff

And then:

    cd ./sql
    go test -v -i -c
    ./sql.test -test.run TestLogic -d testfile
    go tool trace ./sql.test trace.out

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