Thank you for the reminder.

At first, I wanted to analyze the effectiveness of GC through logs.
However, because GC through the stderr output, these logs are mixed in with other output(such as warnings). This make it difficult to handle them automaticaly.

So, i added an `TestIOWrapper` parameter(Not just file streams, but also other io, sockets, buffer and so on) to `set_debug` function in gcmodule.c, to redirect GC logs.

I think this will help developers monitor the GC more easily, for example when they deal with a memory leak.

Of course, the default will remain the same as the previous behavior , log via stderr :)