Bug#395956: Solution Found

[Nikolaos Charitonides <nchar@ath.forthnet.gr>]

The problem was solved, by manualy installing (using a2enmod) the next modules, 
that installation script doesn't install (neither from clean install, nor from apt-
get dist-upgrade). So, after doing a2enmod for each of the next modules and 

auth_anon auth_basic auth_dbm auth_digest authn_alias authn_anon authn_dbd 
authn_dbm authn_default authn_file authz_dbm authz_default authz_groupfile 
authz_host authz_owner authz_user include userdir vhost_alias

And after that /etc/init.d/apache2 force-reload the problem was fixed, apache2 
started and nagios worked fine.