Display console warnings in a debug window too by taking advantage of our custom message handler

[diederik]

With our custom debug message handler, it would also be possible to redirect all output of the console to a error-dialog instead. That way, we can display WARNING error messages in a debug window, or our network window for example.

When we're doing more advanced stuff from this message handler, also make sure the code can't cause recursions. This can be avoided by keeping a global variable "inMessageHandler" variable.

Note though that the kWarning() and kDebug() output can be redirected to a log file or be disabled by default. That way it won't pass our message handler.