Although rarely done, it is possible to configure the logs during
program initialization by invoking the xbt_log_control_set() method
manually. A more conventional way is to use the --log command line
-argument. xbt_init() (called by MSG_init(), gras_init() and friends)
+argument. xbt_init() (called by MSG_init() and friends)
checks and deals properly with such arguments.
\subsection log_use_conf_thres 3.1.1 Threshold configuration