+/*
+ * Launchs (fork-execs) the program described by 'exec'
+ * using the parameters of 'desc' and 'params' to instantiate
+ * it. The created process is attached to the process group 'progrp'.
+ *
+ * After being created and before to be launched, the process
+ * is put in its security environment and its directory is
+ * changed to params->datadir.
+ *
+ * Returns the pid of the created process or -1 in case of error.
+ */