added dotdeb repo

Dotdeb is a repository containing packages to turn your Debian boxes into powerful, stable and up-to-date LAMP servers:

Nginx,
PHP 5.4 and 5.3,
useful PHP extensions : APC, imagick, Pinba, xcache, Xdebug, XHprof…
MySQL 5.5,
Percona toolkit,
Redis,
Zabbix,
Passenger...