check conditions of  make  for equality of variables with an empty value
instead of check definition.
A defined but empty variable under all these conditions results errors.

Another minor facelift:
- s/ALT Linux/ALT/gc (where applicable);
- s/7.0/8.0/g;
- 2017;
- e2k;
- links.

The reason behind this silly patch is that the default URL
can be left alone with no rebuilds neccessary but with the
intranet services delivered through a "captive portal" or
a redirecting proxy; we definitely don't want the canonical
wiki URL, http://www.altlinux.org, blocked by a rule made
for redirecting the default homepage, so let it be another
one which is served but not widely known or linked to.

There are three more variables to adjust the redirect page:
HOMEPAGE, HOMENAME and HOMEWAIT; e.g. live-webkiosk is now
quite a bit more whitelabel.