Use twisted logger for top level exception handlers

[erikjohnston]

As the twisted logger is more likely to report the actual stack trace

[richvdh]

looks sensible.

Is this a thing we should be doing throughout? Why not do the entire file?

Will lines logged this way get recorded with the correct logcontext?

[erikjohnston]

We should think about this a bit more

[richvdh]

FTR #2705 superceded most of this and I think is a better solution. As I wrote there:

I'm not super-keen on using the twisted logger per se, because it means that we lose log categories etc. Nevertheless, it turns out that we can do what the twisted logger does to recover the original Failure, and get the best of both worlds.