Upgrader - various issues learned via CLI

[sbulen]

Fixes #5981 (in conjunction with #5986 )
Fixes #6001

CLI, especially with 1.x, was generating scores of errors.

Changes:

• The basic problem was that the '@' operator still invokes the error handler, and they get logged, even though they are OK. Not a big deal, other than this was masking some REAL issues. Note that although the @ operator still calls the error routine, it temporarily sets the error level to 0, so it is easy to test in the error handler. So, the real errors were...
• Some true undefined errors were buried in there - and not visible via browser upgrades.
• Fixed the utf8 template issue.
• cmdstep0 is the cli version of WelcomeLogin (without a template) & needed to deal with custom_avatar

A subset of these changes are needed in 2.0 as well.

Testing completed...

[sbulen]

That last commit addressed undefined offset issues experienced with most upgrades:

[sbulen]

The last issue I have found during testing is... Interesting...

Via CLI, I am seeing a class of undefined errors that are pretty big & cause functionality gaps - but there is no corresponding gap when the upgrade is run via the browser.

The difference is that the browser "comes up for air" at various points & restarts. And reloads $modSettings... CLI never reloads $modSettings, so the only values it knows are the ones that were there at the start of the upgrade. The loss of functionality is thus worse the further back you go.

I have some thoughts to address. If easily fixed, we're good. If not, I think guidance needs to be that CLI isn't really appropriate for meaningful upgrades across versions.

Some examples:

[sbulen]

Still testing this. Lots of permutations...

Some variations get this at the very end - looking into it:

I suspect this was brought about by the auth_secret changes.

[jdarwood007]

This is why for beyond 2.1 I'm recommending we drop support for upgrading anything other than the previous major and build converters for those. Its going to become more troublesome in the future to maintain being able to upgrade from YabbSE all the way to current.

[sbulen]

Yep...

[sbulen]

This is why for beyond 2.1 I'm recommending we drop support for upgrading anything other than the previous major and build converters for those. Its going to become more troublesome in the future to maintain being able to upgrade from YabbSE all the way to current.

ALSO VERY IMPORTANT... We need to be careful what gets pushed down to 2.0... If we push the same changes down to 2.0.x, we will break those, too. Some may be unavoidable (security-related). But we need to be mindful of the impacts.

[sbulen]

Testing completed.

One minor issue outstanding that will be logged separately.

[sbulen]

Since some of these issues impact current installs, I think we should merge this one asap.