Raise exceptions for HTTP errors, don't try to continue

[zurohki]

• Raise an exception whenever accessing anything fails.
• Add comments to those lines so everyone can see why they're there.

We seem to still be getting into trouble in some places when the server returns an error page - trying to parse the error page and getting breakage. Raising exceptions will make the try/except code do its thing and abort.

[kuhnertdm]

Merged, thank you