[PATCH] pgweb: Add ARCHIVES_FRONT_ADDRESS to allow configuration of archives

Hello,

Domain of messages in pgweb's search is currently hardcoded as postgresql.org
in templates/search/listsearch.html. This patch allows to use another domain
for links to messages in archives in the search function.
Since pgarchives' domain can differ from pgweb's one, a new variable is defined
for that purpose instead of using SITE_ROOT.

Cheers,
-- 
Célestin Matte