Make a copy of __progname on start to avoid setproctitle clobbering it
later. Check if the OS supports __progname and emulate if unavailable.
- from OpenSSH.
Thanks to Paul B. Henson for reporting the setproctitle emulation issue
and Jonas 'Sortie' Termansen for suggesting __progname emulation.
Allow overriding the user and the config file paths for ntpd.
This also adds back --privsep-path from OpenNTPD, which really only
changes the installation instructions from 'make install', since ntpd
always uses the home directory of the ntpd user.
This borrows from the Darren's portable OpenNTPD and from OpenSSL, add
credits and a license.