[development] Incremental upgrades

[Earnie Boyd]

Quoting Neil Drumm <drumm at delocalizedham.com>:

>
> Theoretically, 4.0 straight up to 5.2 in one go should work. All the
> upgrade scripts are in 5.2. However, changes do sometimes break old
> updates. Updates aren't especially tested for this since most core
> developers go straight out of the older versions and stop giving much
> thought to them.
>

But if the updates in update.php is sequential ...

I suppose the real issue is that current update.php isn't able to 
determine which updates have been applied from previous versions.  I 
would like to think that at some future point this resolvable.

Earnie