New debug scheme with explicit debug channels declaration.

diff --git a/windows/msgbox.c b/windows/msgbox.c
index d71a48d..47b2670 100644
--- a/windows/msgbox.c
+++ b/windows/msgbox.c
@@ -16,6 +16,8 @@
 #include "debugstr.h"
 #include "tweak.h"
 
+DEFAULT_DEBUG_CHANNEL(dialog)
+
 /**************************************************************************
  *           MSGBOX_DlgProc
  *