Refactor Thread class

Associate platform OS thread to the Thread class instead of
creating it from ThreadsManager.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/thread.h

@@ -66,6 +66,9 @@ struct SplitPoint {
 
 struct Thread {
 
+  Thread(int id);
+  ~Thread();
+
   void wake_up();
   bool cutoff_occurred() const;
   bool is_available_to(int master) const;
@@ -100,7 +103,7 @@ class ThreadsManager {
      static storage duration are automatically set to zero before enter main()
   */
 public:
-  Thread& operator[](int threadID) { return threads[threadID]; }
+  Thread& operator[](int threadID) { return *threads[threadID]; }
   void init();
   void exit();
 
@@ -123,7 +126,8 @@ public:
 private:
   friend struct Thread;
 
-  Thread threads[MAX_THREADS + 1]; // Last one is used as a timer
+  Thread* timer;
+  Thread* threads[MAX_THREADS];
   Lock splitLock;
   WaitCondition sleepCond;
   Depth minimumSplitDepth;