Detect malformed responses and support isolated responses so we can re-activate the WISIA source.

Some sources are impractical to harvest completely in one session but are amenable to being updated piece by piece. This is mode of operation of this is supported by this change as some responses can be marked as isolated by having their key end in ".isol" and those take part in age-based removal individually.

This usually means that a table of contents or index is fetched together, but updates to the various isolated responses referenced by it are smeared out over larger window of time.

Additionally, we detect the ORA-01000 error code in the HTML responses to retry to requests with out usual exponential back-off strategy.