Bug#721360: debian-installer: warn that blockdev-wipe can be very slow

[Julian Gilbey <jdg@debian.org>]

Package: debian-installer
Version: 20130613

I'm setting up a new install, using guided partitioning with LUKS
encryption.

I have a 750GB hard disk (a somewhat old machine!) and I've twice
restarted it thinking that it had hung on the screen which says
"Erasing data on SCSI1 ...".

I then realised that it's just exceptionally slow.

I suggest that the dialog window should say something along the lines
of "This can take a VERY long time (possibly hours), please be
patient."

Alternatively, if there's a way of saying not to bother wiping the
partition, that could be good for someone who's not overly concerned
that the partition is covered with random bits before they begin.

   Julian