when logging about threading operations, include info about account

in verifydata, when warning about missing threading, print the db file.
otherwise it isn't clear which account this is about

when upgrading account thread storage, pass the logger that has the account
name.

store/threads.go

@@ -735,7 +735,7 @@ func upgradeThreads(ctx context.Context, acc *Account, up *Upgrade) error {
 		t0 := time.Now()
 
 		const batchSize = 10000
-		total, err := acc.ResetThreading(ctx, xlog, batchSize, true)
+		total, err := acc.ResetThreading(ctx, log, batchSize, true)
 		if err != nil {
 			return fmt.Errorf("resetting message threading fields: %v", err)
 		}
@@ -757,7 +757,7 @@ func upgradeThreads(ctx context.Context, acc *Account, up *Upgrade) error {
 		t0 := time.Now()
 
 		const batchSize = 10000
-		if err := acc.AssignThreads(ctx, xlog, nil, 1, batchSize, io.Discard); err != nil {
+		if err := acc.AssignThreads(ctx, log, nil, 1, batchSize, io.Discard); err != nil {
 			return fmt.Errorf("upgrading to threads storage, step 2/2: %w", err)
 		}
 		up.Threads = 2

verifydata.go

@@ -245,9 +245,9 @@ possibly making them potentially no longer readable by the previous version.
 
 			up := store.Upgrade{ID: 1}
 			if err := db.Get(ctxbg, &up); err != nil {
-				log.Printf("warning: getting upgrade record (continuing, but not checking message threading): %v", err)
+				log.Printf("warning: %s: getting upgrade record (continuing, but not checking message threading): %v", dbpath, err)
 			} else if up.Threads != 2 {
-				log.Printf("warning: no message threading in database, skipping checks for threading consistency")
+				log.Printf("warning: %s: no message threading in database, skipping checks for threading consistency", dbpath)
 			}
 
 			mailboxes := map[int64]store.Mailbox{}