upgrade packs

[Gergo Szakal]

DragonFly still lacks binary upgrades which makes upgrades on older
computers a real PITA. While dealing with this in the last few days an
idea popped into my head for at least partially resolving this: upgrade
packs.
These are basically source trees on which buildworld and buildkernel
has already been performed. If one tar's these up and shares them, the
end-user would only have to download and unpack them, followed by an
installkernel/installworld/upgrade sequence. Were these pulled from
git, later updates for the branch from which the whole thing was
generated could easily be pull'd and quickworld/quickkernel could be
performed (I am talking about release branches in the first place).
This way, binary upgrades would partially be resolved, but this needs a
little extra storage space on the mirrors, however this should be no
big concern since my copy here is ~700M uncompressed.

So the whole thing:
-pull from git
- make buildworld
- make buildkernel
- tar up
- share

Opinions?