fix handling of backtrackable C-code in longjmp and other long range cuts.

C/tracer.c

@@ -163,6 +163,9 @@ low_level_trace(yap_low_level_port port, PredEntry *pred, CELL *args)
   LOCK(Yap_heap_regs->low_level_trace_lock);
   sc = Yap_heap_regs;
   vsc_count++;
+  if (vsc_count < 12000)
+    return;
+  jmp_deb(1);
 #ifdef THREADS
   LOCAL_ThreadHandle.thread_inst_count++;
 #endif