Bug#695908: When server host preseed with port number, it failed to get preseed file

[YunQiang Su <wzssyqa@gmail.com>]

Package: debian-installer

For example, we put preseed on http://mirrors:9999/pxe.seed,
and dns set domain as example.com, then debian-installer
will try to download

http://mirrors:9999.example.com/pxe.seed

but not
http://mirrors.example.com:9999/pxe.seed

--
YunQiang Su