Extracted intrusive_ref_counter from Boost.Log. The extracted version supports customizing the reference counter nature, two policies provided: thread_unsafe_counter and thread_safe_counter.

[SVN r85535]

test/Jamfile.v2

@@ -21,6 +21,7 @@ import testing ;
           [ run get_deleter_test.cpp ]
           [ run intrusive_ptr_test.cpp ]
           [ run intrusive_ptr_move_test.cpp ]
+          [ run intrusive_ref_counter_test.cpp ]
           [ run atomic_count_test.cpp ]
           [ run lw_mutex_test.cpp ]
           [ compile-fail shared_ptr_assign_fail.cpp ]