generate errors from bad <logfile> sections earlier

[freddrake]

• allow disallowed combinations of options be be identified
  and reported earlier (before any logfile handlers are created, and
  before any files are opened)

• ensure DataConversionError is not converted to
  ConfigurationSyntaxError when a section end is loaded

[freddrake]

Risks: Changes can affect 3rd-party handlers that derive from ZConfig.components.logger.handlers.FileHandlerFactory.

I'd expect the real risk of this is low, but can be difficult to predict, and it could take some time for affected users to report problems.

[mgedmin]

LGTM, but this might need a big version bump and a changelog notice about the earlier point of binding of sys.stdout/sys.stderr.

[jamadden]

LGTM. I like the earlier error reporting, and I like not changing exception types unnecessarily (though I don't think I saw any tests that specifically check the type of exception?).

I agree that this needs a prominent change note and is probably technically incompatible enough that it deserves a major bump.

[freddrake]

Agree with you both on needing a change note; realized I'd not done that while in the shower.

The earlier change, with delay and encoding support, included an update to 3.4.0, so I think the feature-added bump is fine. Were you thinking this should be a backward-incompatibility bump (to 4.0.0) instead?

[mgedmin]

I don't know. To me 3.3.x -> 3.4.0 is not scary, nobody's going to carefully look the changelog for such an update. But then the chances of this being a breaking change also seem small, so maybe that's fine?

[freddrake]

On thinking further, the change in capture time of the STDOUT and STDERR streams is a detail tied to the implementation changes. I'm going to treat that as unintentional, and adjust so the capture time remains at handler construction.

[freddrake]

Original capture time for stderr, stdout restored in commit f3fe237.

Added note to change history.

Still need tests that exceptions aren't changed inappropriately.

[freddrake]

Done with changes; again ready for review.