Improve debugging and tracing information

This patch reviews various debug and informational messages, making more
uniform use of tracing, and extends the monitoring http server with
useful information like an index and a queue dump.

internal/courier/procmail.go

@@ -26,14 +26,14 @@ type Procmail struct {
 }
 
 func (p *Procmail) Deliver(from string, to string, data []byte) (error, bool) {
-	tr := trace.New("Procmail", "Deliver")
+	tr := trace.New("Procmail.Courier", to)
 	defer tr.Finish()
 
 	// Sanitize, just in case.
 	from = sanitizeForProcmail(from)
 	to = sanitizeForProcmail(to)
 
-	tr.LazyPrintf("%s -> %s", from, to)
+	tr.Debugf("%s -> %s", from, to)
 
 	// Prepare the command, replacing the necessary arguments.
 	replacer := strings.NewReplacer(
@@ -97,6 +97,7 @@ func (p *Procmail) Deliver(from string, to string, data []byte) (error, bool) {
 		return err, permanent
 	}
 
+	tr.Debugf("delivered")
 	return nil, false
 }