message: Remove mutex and switch to atomic bool in checkqueue.h
diff: #define BITCOIN_CHECKQUEUE_H
  #include <algorithm>
  +#include <atomic>
  #include <vector>
  #include <boost/foreach.hpp>
  @@ -60,11 +61,8 @@ private:
  */
  unsigned int nTodo;
  - //! mutex to protect fQuit.
  - boost::mutex mutex_fQuit;
  -
  //! Whether we're shutting down.
  - bool fQuit;
  + std::atomic<bool> fQuit;
  //! The maximum number of elements to be processed in one batch
  unsigned int nBatchSize;
  @@ -90,7 +88,6 @@ private:
  queue.clear();
  condMaster.notify_one();
  }
  - boost::mutex::scoped_lock lock(mutex_fQuit);
  if (fQuit && !fMaster) {
  nTodo = 0;
  queue.clear();
  @@ -109,7 +106,6 @@ private:
  if (fMaster)
  fAllOk = true;
  // return the current status
  - boost::mutex::scoped_lock lock(mutex_fQuit);
  fQuit = false; // reset the flag before returning
  return fRet;
  }
  @@ -160,7 +156,6 @@ public:
  //! Quit execution of any remaining checks.
  void Quit(bool flag = true)
  {
  - boost::mutex::scoped_lock lock(mutex_fQuit);
  fQuit = flag;
  }
  