Revise the implementation of OP_Once so that it is smaller, faster, and uses
less memory.  This also fixes an obscure bug introduced 3 days ago by check-in
[5990a1bdb4a073].

FossilOrigin-Name: 6bf5ba10d28f1b0a32aa9a560ae3143a1235eadb
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index dbb18a7..ebae7e5 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -2896,7 +2896,6 @@
   int nTab;            /* Number of previously allocated VDBE cursors */
   int nMem;            /* Number of memory cells used so far */
   int nSet;            /* Number of sets used so far */
-  int nOnce;           /* Number of OP_Once instructions so far */
   int nOpAlloc;        /* Number of slots allocated for Vdbe.aOp[] */
   int szOpAlloc;       /* Bytes of memory space allocated for Vdbe.aOp[] */
   int iFixedOp;        /* Never back out opcodes iFixedOp-1 or earlier */
@@ -3230,6 +3229,7 @@
   int (*xTestCallback)(int);        /* Invoked by sqlite3FaultSim() */
 #endif
   int bLocaltimeFault;              /* True to fail localtime() calls */
+  int iOnceResetThreshold;          /* When to reset OP_Once counters */
 };
 
 /*