Removing upgrade

[Karsten Behrmann]

> I'll be on your side if there is any push back :)

There is.

Surprisingly, people were actually still using this in some cases.
Mostly as a "clobber install" if they somehow managed to trash
their binaries, sometimes as a quick-and-dirty update-to-current.

Concensus (as far as I see on IRC) seems to be this:

We re-add the feature, but we name it "restore" rather than "update",
and do not advertise that it is in any way supposed to work as a
method to update a system.
Instead, it is a fixit option (potentially stuffed somewhere inside
an appropriate submenu) that overwrites part of your install with
fresh files from package.
We should probably prefix a warning dialog "may eat your cat/dog/aunt".

We didn't yet agree on what to do with /etc, suggestions include:
a) Keep the current code
b) Leave /etc untouched entirely
c) Write fresh files to /etc/$file.restore.$date and leave originals alone
d) Attempt to run mergemaster
e) Any combination of the above

Personally, I think we want something between b) and c).
I don't see us maintaining a proper "safe merge" thing anytime soon,
so we shouldn't try. The current code is dangerous and should be scrapped.
If we're feeling particularly luxurious, we could let the user decide
which areas they want protected/clobbered/augmented, potentially by
dropping them into an editor for a simple filter definition file.

If people want to still use this to update between -current commits,
I guess we can't stop them, but it should not be an intended functionality.
The less code we need for this the better: sysinstall is not really in the
business of replacing mergemaster, our energies at writing and understanding
code are better spent elsewhere.

So Far,
  Karsten "BearPerson" Behrmann