Change Log4cxxConfig.xml min level to "warn"

Most Log4cxx logging is done at the INFO level.  This makes the log
file massive, and hides undiscovered errors.  To fight this trend,
the default minimum reporting level was changed to WARN.  This way,
WARNings and ERRors are easy to see in the log file (theyre not
buried).

To see the INFO level log statements, the commit can be undone by
changing the text "warn" to "all"