0.2: Improve error handling

[nrc]

Debugging and handling errors is sub-optimal. Our errors are pretty good for the general case, and for just printing an error to a log or whatever, but if you're actually trying to fix bugs or handle the errors programatically, then they are not ideal.

A concrete example is that if an error is thrown while a transaction has not been committed/dropped, then we panic and the underlying error is lost. I think there are other places where an error causes another error and we lose underlying info.