Ignore SIGTERM when firing stop and signal.term

Move firing "server.stop" and "server.signal.term" triggers beyond
setting SIGTERM action to SIG_IGN in main().

This way handler commands for these triggers don't receive SIGTERM with
the rest of the process group and don't possibly terminate before doing
their work. E.g. snmptrap manages to send the notifications.
Update Stripped-User-Name, too.

And do one loop, rather than 3.  It's a bit more efficient.
Fix debug_name for policies
Add and document reject_delay of fractional seconds
Add FreeRADIUS-Response-Delay-USec
Actually check the path specified by configure
Fix configure argument names
Lock thread_pool.wait_mutex before forking to avoid a race condition between rad_fork, rad_waitpid and reap_children.

There is a race condition that can occur under high load where a child is reaped before being added to the waiters list.