sql: avoid copying mutex
sql: avoid copying mutex

go1.7 vet complains about:

  sql/pgwire_internal_test.go:85: assignment copies lock value to lease:
  sql.LeaseState contains sync.Mutex

vivekmenezes/cockroach,vivekmenezes/cockroach,glycerine/cockroach,glycerine/cockroach,arjun4084346/cockroach,maxlang/cockroach,vivekmenezes/cockroach,paperstreet/cockroach,cockroachdb/cockroach,arjun4084346/cockroach,vivekmenezes/cockroach,vaibhavarora/cockroach,arjun4084346/cockroach,maxlang/cockroach,veteranlu/cockroach,arjun4084346/cockroach,sunya123/cockroach,cockroachdb/cockroach,paperstreet/cockroach,glycerine/cockroach,glycerine/cockroach,veteranlu/cockroach,cockroachdb/cockroach,petermattis/cockroach,cockroachdb/cockroach,sunya123/cockroach,maxlang/cockroach,maxlang/cockroach,paperstreet/cockroach,paperstreet/cockroach,veteranlu/cockroach,arjun4084346/cockroach,sunya123/cockroach,petermattis/cockroach,vaibhavarora/cockroach,sunya123/cockroach,cockroachdb/cockroach,vaibhavarora/cockroach,cockroachdb/cockroach,vivekmenezes/cockroach,arjun4084346/cockroach,paperstreet/cockroach,sunya123/cockroach,petermattis/cockroach,glycerine/cockroach,paperstreet/cockroach,veteranlu/cockroach,paperstreet/cockroach,glycerine/cockroach,maxlang/cockroach,vaibhavarora/cockroach,veteranlu/cockroach,vaibhavarora/cockroach,sunya123/cockroach,maxlang/cockroach,veteranlu/cockroach,veteranlu/cockroach,vaibhavarora/cockroach,cockroachdb/cockroach,arjun4084346/cockroach,paperstreet/cockroach,glycerine/cockroach,glycerine/cockroach,petermattis/cockroach,vaibhavarora/cockroach,petermattis/cockroach,veteranlu/cockroach,sunya123/cockroach,petermattis/cockroach,vaibhavarora/cockroach,maxlang/cockroach,vivekmenezes/cockroach,sunya123/cockroach,petermattis/cockroach,petermattis/cockroach,arjun4084346/cockroach,cockroachdb/cockroach,vivekmenezes/cockroach,maxlang/cockroach,vivekmenezes/cockroach