cmd/mbf: disable threshold by default

This is not very useful.

Signed-off-by: Ophestra <cat@gensokyo.uk>

cmd/mbf/main.go

@@ -62,11 +62,14 @@ func main() {
 			return
 		}
 		if cache, err = pkg.Open(ctx, msg, flagCures, base); err == nil {
-			if flagTShift < 0 || flagTShift > 31 {
-				flagTShift = 31
-			}
+			if flagTShift < 0 {
+				cache.SetThreshold(0)
+			} else if flagTShift > 31 {
+				cache.SetThreshold(1 << 31)
+			} else {
 				cache.SetThreshold(1 << flagTShift)
 			}
+		}
 		return
 	}).Flag(
 		&flagVerbose,
@@ -82,7 +85,7 @@ func main() {
 		"Directory to store cured artifacts",
 	).Flag(
 		&flagTShift,
-		"tshift", command.IntFlag(31),
+		"tshift", command.IntFlag(-1),
 		"Dependency graph size exponent, to the power of 2",
 	)