more fixes to debugger: make l and s option do what they are supposed to

do.
fix k and t, they had been broken.
Ideas:
DebugOn is now in the system and can disable spypoints.
Have an extra flag to distinguish fast (t,z,k) and slow(l,s) jumping.

C/tracer.c

@@ -164,6 +164,10 @@ 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 < 88000)
+    return;
+  if (vsc_count == 88483LL)
+    jmp_deb(1);
 #ifdef THREADS
   Yap_heap_regs->thread_handle[worker_id].thread_inst_count++;
 #endif