Fix memory leak in freezer implementation

It turns out we were only notifying plugins of freezer commits and
cleaning up our record when the block being processed was greater
than MAX_UINT64.

So, uh, never.

core/rawdb/plugin_hooks.go

@@ -39,7 +39,7 @@ func PluginCommitUpdate(pl *plugins.PluginLoader, num uint64) {
 	if freezerUpdates == nil { freezerUpdates = make(map[uint64]map[string]interface{}) }
 	min := ^uint64(0)
 	for i := range freezerUpdates{
-		if min < i { min = i }
+		if min > i { min = i }
 	}
 	for i := min ; i < num; i++ {
 		update, ok := freezerUpdates[i]