Causes Radiator to start printing log message at or below the
given log level. The number n can be 0 to 5 inclusive. Each new Monitor
connection starts out at level 0 (ERR level). Level 4 is DEBUG level.
After setting a new Trace level, Radiator will send all log messages at or
below that level on the Monitor connection.
If a TRACE_USERNAME is
in force, only messages that result from requests from that specific
User-Name will be printed.