Add speckseq field to specklists so we can track derived versions.

Add seed counter to struct stuff.

src/specks.h

@@ -103,6 +103,7 @@ struct specklist {
   char *text;
   int subsampled;	/* subsampling ("every") factor applied already */
   int used;		/* "used" clock, for mem purges */
+  int speckseq;		/* sequence number, for tracking derived specklists */
   enum SpecialSpeck special;
   struct specklist *freelink; /* link on free/scrap list */
 };
@@ -295,6 +296,8 @@ struct stuff {
   int usertrange;
   double utmin, utmax, utwrap;	/* user-supplied time range */
 
+  int speckseq;		/* sequence-number seed */
+
   /* async command streams */
 #define MAX_ASYNC 8
   FILE *asyncmd[MAX_ASYNC];