We want per-blog traffic stats.

Apache noblogs is configured with a single virtualhost, we cannot use the
virtualhost name (%v) for these stats, because everything will appear as
noblogs.org .

We cannot even use the Host header (%{Host}i) because the virtualhost wildcard
configuration allows for bogus blog names (e.g. cavalle55e.noblogs.org instead
of cavallette.noblogs.org).

With this map nginx can lookup a valid blog name (or default to noblogs.org for
invalid names) and pass it to apache with an internal header (e.g.
X-AI-Noblogs-Site ). Apache will then use this header to produce correct stats.

Signed-off-by: shammash <shammash@autistici.org>