Core/Thread: Fix race condition in FreezeDetectorRunnable

Fix race condition by replacing a static volatile uint32 with proper atomic thread-safe ACE_Atomic_Op<ACE_Thread_Mutex, uint32>, incremented in WorldRunnable::run() at each world loop and read in FreezeDetectorRunnable::run().

Helgrind log:
 Possible data race during read of size 4 at 0x2400D54 by thread #12
 Locks held: none
    at 0x100FEA6: FreezeDetectorRunnable::run() (Master.cpp:106)
    by 0x1637892: ACE_Based::Thread::ThreadTask(void*) (Threading.cpp:186)
    by 0x518F555: ACE_OS_Thread_Adapter::invoke() (OS_Thread_Adapter.cpp:103)
    by 0x4C2B5AD: mythread_wrapper (hg_intercepts.c:219)
    by 0x61DAB4F: start_thread (pthread_create.c:304)
    by 0x6C69A7C: clone (clone.S:112)

 This conflicts with a previous write of size 4 by thread #9
 Locks held: none
    at 0x100C23E: WorldRunnable::run() (WorldRunnable.cpp:55)
    by 0x1637892: ACE_Based::Thread::ThreadTask(void*) (Threading.cpp:186)
    by 0x518F555: ACE_OS_Thread_Adapter::invoke() (OS_Thread_Adapter.cpp:103)
    by 0x4C2B5AD: mythread_wrapper (hg_intercepts.c:219)
    by 0x61DAB4F: start_thread (pthread_create.c:304)
    by 0x6C69A7C: clone (clone.S:112)