keep last Incident in RAM to help debug disk-full conditions

[Brian Warner]

As mentioned in #144, it'd be nice if disk-full situations were easier to debug. The idea would be to record the last Incident as a single string (serialized+compressed) in memory, and to make in-memory Incidents available to the incident-gatherer (just like on-disk Incident files are). It might also be useful to make flogtool tail have a mode or a message to indicate that an Incident is available, and to fetch its contents (since launching an incident-gatherer just to fetch a single Incident is a hassle).

We should think about when this would actually be useful, though. I think that mostly we need to remember that a disk-full situation occurred, so we can rule out other weird problems.

[davidsarah]

Replying to warner:

I think that mostly we need to remember that a disk-full situation occurred, so we can rule out other weird problems.

+1. A serialized-compressed incident would be nice to have, to allow debugging how we respond to disk full. But if it is hard to do that, a "disk was full" flag is useful on its own.