Install of package from Experimental? - was installing GRASS7

[Zenaan Harkness]

Anyone know why my Debian experimental install of GRASS7 fails?
TIA
Zenaan

---------- Forwarded message ----------
From: Zenaan Harkness <zen at freedbms.net>
Date: Sun, 28 Jun 2015 01:42:59 +0000
Subject: installing GRASS7
To: grass-user at lists.osgeo.org

I'm on Debian Jessie (stable), have not used GIS software before and
want to learn GRASS so it makes sense to me to start with GRASS7
rather than 6.4 (which is available in Debian).

I tried without success the instructions to install GRASS7 from
experimental here:
https://wiki.debian.org/DebianExperimental

I added this to sources.list:
deb http://ftp.au.debian.org/debian/ experimental main contrib

Then:
apt-get update
apt-get -t experimental install grass-core grass-gui

First it failed, so I installed grass from stable and now I can run this:
$ grass --version
GRASS GIS 6.4.4
cat: /usr/lib/grass64/etc/license: No such file or directory

So firstly, can someone tell me what that last line of output is (it
looks very odd to coming out of a Debian package)?

Now when I try:
apt-get -t experimental install grass-core grass-gui
I get the following output:
Reading package lists... Done
Building dependency tree
Reading state information... Done
grass-core is already the newest version.
grass-gui is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 6 not upgraded.

Can anyone help here - I'd really like to start on GRASS7, if possible
(on Debian stable - would that normally be a "backport" or an
"update"?).

Thanks heaps,
Zenaan