Added better dovecot version detection in Debian and Ubuntu installer.

Till Brehm

2014-10-18 1fc360dfaf61613735cb635c8e905af2b089cf68

 install/sql/incremental/upd_0052.sql

New file
@@ -0,0 +1 @@
ALTER TABLE `client` ADD `default_slave_dnsserver` INT( 11 ) UNSIGNED NOT NULL DEFAULT '1' AFTER `limit_dns_zone`;