Add a wrapper for the very basic mutex locking we make use of

Installation/include/CGAL/mutex.h

@@ -0,0 +1,18 @@
+#ifndef CGAL_MUTEX_H
+#define CGAL_MUTEX_H
+
+#include <CGAL/config.h>
+
+#ifdef BOOST_MSVC
+#include <mutex>
+#define CGAL_MUTEX std::mutex
+#define CGAL_SCOPED_LOCK(M) std::unique_lock<std::mutex> scoped_lock(M)
+
+#else
+#include <boost/thread/mutex.hpp>
+#define CGAL_MUTEX boost::mutex
+#define CGAL_SCOPED_LOCK(M) boost::mutex::scoped_lock scoped_lock(M)
+
+#endif
+
+#endif // CGAL_MUTEX_H