systemd units added

Release: 4
Drop HTTPD_CONF and HTTPD_OPTS support from init/sysconfig

HTTPD_CONF support was plain wrong. Seems just copied from Apache
httpd.init and uses a command-line option which is not supported
by nginx. And adds the option to the 'killproc' command too. This
just could not work.

HTTPD_OPTS could work, but was not documented, was named wrong
and seems quite useless (nginx command-line options do not provide
any useful functionality).
Set up the 'nginx.service' systemd unit alias

This makes 'service nginx status' and similar calls useful,
while keeping the standard/light/perl/mail service separation.

This alias will be set up when nginx-standard is installed, but may be
manually changed to point to any of the other variants.
The post NOT message improved