use std::unordered_set instead of boost::unordered_set. Segfault on boost 1.65.1

Author: hieuhoang

moses2/HypothesisColl.cpp

@@ -254,6 +254,8 @@ void HypothesisColl::Delete(const HypothesisBase *hypo)
   //cerr << "hypo=" << hypo << " " << m_coll.size() << endl;
 
   size_t erased = m_coll.erase(hypo);
+  //cerr << "erased=" << erased << " " << m_coll.size() << endl;
+
   UTIL_THROW_IF2(erased != 1, "couldn't erase hypo " << hypo);
 }
 

moses2/HypothesisColl.h

@@ -5,6 +5,7 @@
  *      Author: hieu
  */
 #pragma once
+#include <unordered_set>
 #include <boost/unordered_set.hpp>
 #include "HypothesisBase.h"
 #include "MemPoolAllocator.h"
@@ -53,7 +54,7 @@ class HypothesisColl
   std::string Debug(const System &system) const;
 
 protected:
-  typedef boost::unordered_set<const HypothesisBase*,
+  typedef std::unordered_set<const HypothesisBase*,
           UnorderedComparer<HypothesisBase>, UnorderedComparer<HypothesisBase>,
           MemPoolAllocator<const HypothesisBase*> > _HCType;