detect the ubuntu version based on /etc/os-release

Uwe Merbeth

2016-05-09 f5daecadf5846ff0b2d512e6a1a47f17342fe02b

 install/sql/incremental/upd_0052.sql

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