Merge branch 'stable-3.1'

install/dist/conf/centos72.conf.php

install/dist/lib/fedora.lib.php

install/dist/lib/gentoo.lib.php

install/dist/lib/opensuse.lib.php

install/install.php

install/lib/install.lib.php

install/lib/installer_base.lib.php

install/sql/incremental/upd_0081.sql

install/sql/ispconfig3.sql

install/tpl/debian6_dovecot-sql.conf.master

install/tpl/debian_dovecot-sql.conf.master

install/tpl/debian_dovecot2.conf.master

install/tpl/debian_postfix.conf.master

install/tpl/fedora_amavisd_conf.master

install/tpl/fedora_dovecot-sql.conf.master

install/tpl/fedora_dovecot2.conf.master

install/tpl/fedora_postfix.conf.master

install/tpl/gentoo_postfix.conf.master

install/tpl/opensuse_amavisd_conf.master

install/tpl/opensuse_dovecot-sql.conf.master