use separate log statements for sequencer diagnostics

The output of the previous panic message was way too large, and was
truncated. So this changes to separate logs of each of the things that
we'd like to see.

message/sequencer.go

@@ -408,15 +408,32 @@ func (w *Sequencer) Step() error {
 				// with one exception: messages with zero-valued Clocks are not
 				// expected to be consistently ordered on clock.
 				// In QueueUncommitted we synthetically assigned a clock value.
-				panic(fmt.Sprintf("ring clock <= emit.minClock\n%+v", map[string]interface{}{
+				// Log a bunch of diagnostics using separate
+				log.WithFields(log.Fields{
 					"uuid":          uuid,
-					"message":       w.Dequeued,
 					"dequeuedClock": w.dequeuedClock,
-					"offsets":       w.offsets,
-					"partials":      w.partials,
-					"pending":       w.pending,
-					"emit":          w.emit,
-				}))
+					"emit":          fmt.Sprintf("%+v", w.emit),
+					"partialsCount": len(w.partials),
+					"pendingCount":  len(w.pending),
+				}).Error("ring clock <= emit.minClock (will log diagnostics then panic)")
+				log.WithField("offsets", w.offsets).Error("sequencer offsets")
+				log.WithField("dequeued", w.Dequeued).Error("dequeued message")
+
+				for producer, partial := range w.partials {
+					log.WithFields(log.Fields{
+						"producer": producer,
+						"partial":  partial,
+					}).Error("partials")
+				}
+				var i = 0
+				for pending, _ := range w.pending {
+					log.WithFields(log.Fields{
+						"i":       i,
+						"pending": pending,
+					}).Error("pending")
+					i++
+				}
+				panic("ring clock <= emit.minClock")
 			}
 		} else if w.dequeuedClock > w.emit.maxClock {
 			continue // ACK'd clock tells us not to commit.