T: bug fixes for the T cache

- 'busy' has to be handled in a more atomic fashion to avoid crazy
  runtime race conditions
- the basic simulator is too fast sometimes; rewrite the accesses to
  the T cache to avoid there again crazy behaviors

Hopefully that's better...

common/utils/T/T.c

@@ -31,6 +31,12 @@ volatile int _T_freelist_head;
 volatile int *T_freelist_head = &_T_freelist_head;
 T_cache_t *T_cache;
 
+#if BASIC_SIMULATOR
+/* global variables used by T_GET_SLOT, see in T.h */
+volatile uint64_t T_next_id;
+volatile uint64_t T_active_id;
+#endif
+
 static void get_message(int s)
 {
   char t;