Add new "nghosts" field for keeping animation history (trails).

src/specks.h

@@ -235,6 +235,7 @@ struct stuff {
 
   int used;		/* global "used" clock, for LRU purging */
   struct specklist *scrap; /* stuff to be deleted when it's safe */
+  int nghosts;		/* keep recent ghost snapshots of dynamic data */
 
   /* async command streams */
 #define MAX_ASYNC 8