Add vm_memory_calculation_strategy to ctl status

How total amount of memory is computed is an important
piece of information: what the runtime reports and what tools
such as 'ps' report will differ.

http://erlang.org/pipermail/erlang-questions/2012-September/069337.html is
a good source of information on some of the discrepancies.

Author: michaelklishin

src/rabbit.erl

@@ -640,7 +640,8 @@ status() ->
           {erlang_version,       erlang:system_info(system_version)},
           {memory,               rabbit_vm:memory()},
           {alarms,               alarms()},
-          {listeners,            listeners()}],
+          {listeners,            listeners()},
+          {vm_memory_calculation_strategy, vm_memory_monitor:get_memory_calculation_strategy()}],
     S2 = rabbit_misc:filter_exit_map(
            fun ({Key, {M, F, A}}) -> {Key, erlang:apply(M, F, A)} end,
            [{vm_memory_high_watermark, {vm_memory_monitor,