Revert last change in debug.h, use "??" instead of ((__const char *)0)

Replace DBG() statements with TRACE() in libxfcegui4 and xfwm4 because it was generating far too much logs in simple debug mode (use --enable-debug=full to get full traces)
Add params to TRACE() (just like in DBG())
Remove trailing CR in log messages


(Old svn revision: 686)