Updated installation images for Debian Ports 2020-04-19

Hi!

I just uploaded updated installation images 2020-04-19 for the
following Debian Ports architectures [1]:

 * alpha
 * hppa
 * ia64
 * m68k
 * powerpc
 * ppc64
 * sparc64

These images should finally fix the installation process on Apple
PowerMacs and PowerBooks compatible with GRUB, so basically every
Macintosh using the New World ROM [2].

One user already reported a successful installation on his PowerMac
G5 and I expect installations to work fine on 32-bit machines, i.e.
G3 and G4 as well. But I'm looking forward to more feedback.

Another important improvement to debian-installer is that the mirror
setup now allows to select the preferred mirror from a list instead
having to enter that information manually. Unfortunately, there are
only a few mirrors, namely in Germany and South Korea which can be
chosen from. So don't be surprised that the list is short.

Otherwise, the images contain the usual improvements like a new kernel
and a fresh base system.

Thanks,
Adrian

> [1] https://cdimage.debian.org/cdimage/ports/2020-04-19/
> [2] https://en.wikipedia.org/wiki/New_World_ROM