Several S4 services log many many "Unhandled error in Deferred" messages

[exarkun]

Something is going wrong. However, there's a bug in the logging system so there's no additional details logged with these errors. They're also difficult to reproduce locally.

Supposedly the logging issue is fixed upstream in the latest Twisted release. If we upgrade to that, maybe production logs will become more useful. There are some incompatibilities with the latest Twisted release to fix first, though.

[exarkun]

We now at least get tracebacks thanks to monkey-patching in a fix for http://twistedmatrix.com/trac/ticket/8860

I haven't observed the problem since deploying this... but I also haven't been reading all the logs. Getting errors into a monitoring system would make it easy to put this on the back burner (and then get a notification when it's time to investigate again).