split syslogd.c file into GPLv3 and ASL 2.0 parts

This is just the initial commit, we need to shuffle more
code, but need to check carefully that what we do is correct
(proper code ownership).

See also: https://github.com/rsyslog/rsyslog/issues/82
last commit introduced regression, fixing this
cleanup
rewrite usage() function
refactor
refactor
refactor
cleanup, new interfaces
cleanup: remove no longer used code